Temporal Proximity Not Required: First Circuit Clarifies Causation and Pretext Under Puerto Rico Law 115

Introduction

In Mercado v. Hyannis Air Service, Inc., No. 23-1744 (1st Cir. Sept. 22, 2025), the First Circuit vacated summary judgment against a former Cape Air cross-train agent, Erasto Román Mercado, on his Puerto Rico Law 115 retaliation claim and remanded for trial. The case presents a significant clarification for retaliation litigation under Puerto Rico’s Whistle-Blower Act (Law 115): a plaintiff need not rely solely on close temporal proximity to establish causation. Instead, courts must consider the totality of the circumstances, including inconsistent or shifting explanations offered by the employer, when assessing whether the protected activity was causally linked to the adverse action.

The dispute arose after Román suffered a workplace injury in April 2017 that was followed by delayed filings with Puerto Rico’s State Insurance Fund (the Fund), medical leave, and ultimately a termination letter sent in June 2019 but made retroactively effective as of May 21, 2019. Román alleged that Cape Air retaliated against him for seeking benefits and treatment with the Fund, a protected activity under Puerto Rico law. The district court granted summary judgment to the employer, concluding the five-month gap between the protected activity and the discharge defeated causation and that, in any event, the employer’s reasons were not pretextual. The First Circuit disagreed, emphasizing both the proper summary judgment lens and the breadth of permissible circumstantial proof of causation and pretext.

Key Timeline

April 16, 2017: Workplace injury when the aircraft cabin door support unhinged and hit Román’s forehead; pilot files an incident report noting missing safety clips.
2017–2019: Employer fails to timely file a Work Accident Report with the Fund; eventually filed in March 2019 and amended in May 2019.
November 30, 2018: Román reports to the Fund and begins treatment; later placed on FMLA leave (Dec. 5, 2018–Feb. 27, 2019).
February–April 2019: Ongoing Fund treatment and post-surgical rest orders; return to work projected for June 13, 2019.
April 29–30, 2019: Supervisor informs HR about planned meeting to discuss termination; meeting does not occur.
June 10, 2019: HR sends termination letter, retroactive to May 21, 2019, citing failure to keep employer informed.
District court: Grants summary judgment to employer on Law 115, finding lack of causation and no pretext.
First Circuit: Vacates and remands for further proceedings.

Summary of the Opinion

The First Circuit held that the district court erred by treating “close temporal proximity” as a necessary condition for proving causation at the prima facie stage of a Law 115 retaliation claim. While timing can suffice in some cases, causation can also be shown through other circumstantial evidence—such as employer antagonism, inconsistencies, contradictions, or shifting explanations for a discharge. Applying Puerto Rico’s statutory direction to interpret employment discrimination and retaliation laws consistently with federal law, the court used the familiar McDonnell Douglas burden-shifting framework.

The court further held that Cape Air’s shifting rationales for Román’s termination—particularly the disparity between the reasons stated in the termination letter (failure to keep employer informed) and the later-litigation rationale (operational needs/third agent coverage), and contradictions about the timing of the decision—create genuine disputes of material fact on pretext and, consequently, on causation. Because summary judgment precludes weighing credibility or resolving factual disputes, the case must go to a jury.

The judgment was vacated solely as to Law 115; the dismissal of Román’s other claims (including his Law 80 wrongful discharge claim) remains in place.

Analysis

Precedents Cited and Their Influence

Puerto Rico interpretive statutes (29 L.P.R.A. §§ 122l, 123a): The court emphasized that Puerto Rico law mandates consistency with federal employment discrimination and retaliation jurisprudence unless the Puerto Rico statute expressly demands a different reading. This is the conduit for applying the McDonnell Douglas framework to Law 115 claims.
McDonnell Douglas Corp. v. Green, 411 U.S. 792 (1973): Frames the burden-shifting sequence: (1) plaintiff’s prima facie case; (2) employer’s legitimate, non-retaliatory reason; (3) plaintiff’s proof of pretext.
Rivera-Rivera v. Medina & Medina, Inc., 898 F.3d 77 (1st Cir. 2018); Rodríguez-Severino v. UTC Aerospace Sys., 52 F.4th 448 (1st Cir. 2022): Confirm that Law 115 retaliation analysis substantially overlaps with Title VII antiretaliation standards.
Calero-Cerezo v. DOJ, 355 F.3d 6 (1st Cir. 2004); Colburn v. Parker Hannifin/Nichols Portland Div., 429 F.3d 325 (1st Cir. 2005): The district court relied on these to hold that a five-month gap defeats causation when relying solely on timing. The First Circuit distinguished them: temporal proximity alone must be “very close,” but lack of closeness is not fatal where other evidence supports causation.
Clark County School District v. Breeden, 532 U.S. 268 (2001): Establishes that timing alone requires “very close” proximity. Mercado reaffirms this point but underscores that temporal proximity is not the only route to causation.
Stratton v. Bentley Univ., 113 F.4th 25 (1st Cir. 2024); Kinzer v. Whole Foods Market, Inc., 99 F.4th 105 (1st Cir. 2024): Timing can satisfy the light prima facie burden; Mercado clarifies that causation may also rest on other circumstantial evidence.
Che v. MBTA, 342 F.3d 31 (1st Cir. 2003): Acknowledges multiple avenues to prove causation beyond timing; cited to support full-record causation analysis.
Kengerski v. Harper, 6 F.4th 531 (3d Cir. 2021); Adebiyi v. South Suburban College, 98 F.4th 886 (7th Cir. 2024); Kwan v. Andalex Group, LLC, 737 F.3d 834 (2d Cir. 2013): Cross-circuit authority that causation can be inferred from employer antagonism, ambiguous statements, differential treatment, and especially from weaknesses or contradictions in the employer’s stated reasons.
Texas Dep’t of Community Affairs v. Burdine, 450 U.S. 248, 255 n.10 (1981); Soto-Feliciano v. Villa Cofresí Hotels, Inc., 779 F.3d 19 (1st Cir. 2015): Evidence proving pretext can simultaneously establish causation; showing pretext often means the plaintiff has met the lighter prima facie causation burden.
Domínguez-Cruz v. Shuttle Caribe, Inc., 202 F.3d 424 (1st Cir. 2000); Collazo-Rosado v. Univ. of P.R., 765 F.3d 86 (1st Cir. 2014); Rodríguez-Cardi v. MMM Holdings, Inc., 936 F.3d 40 (1st Cir. 2019); Vélez v. Thermo King de P.R., Inc., 585 F.3d 441 (1st Cir. 2009): Shifting, inconsistent, or contradictory reasons for termination are classic evidence of pretext and can defeat summary judgment.
O’Horo v. Boston Medical Center Corp., 131 F.4th 1 (1st Cir. 2025): States the operative pretext test: whether the employer’s reasons are riddled with “weaknesses, implausibilities, inconsistencies, incoherencies, or contradictions” such that a reasonable factfinder could deem them unworthy of credence.
Summary judgment standards: The First Circuit invoked familiar guardrails: Quintana-Dieppa v. Dep’t of the Army, 130 F.4th 1 (1st Cir. 2025); Dusel v. Factory Mutual Ins., 52 F.4th 495 (1st Cir. 2022); Greenburg v. Puerto Rico Maritime Shipping Auth., 835 F.2d 932 (1st Cir. 1987); Planadeball v. Wyndham Vacation Resorts, Inc., 793 F.3d 169 (1st Cir. 2015); Cherkaoui v. City of Quincy, 877 F.3d 14 (1st Cir. 2017); Sánchez v. Alvarado, 101 F.3d 223 (1st Cir. 1996); Doe v. Trustees of Boston College, 892 F.3d 67 (1st Cir. 2018).

Legal Reasoning

The court applied Puerto Rico Law 115 through the McDonnell Douglas rubric, which is used for Title VII retaliation claims and, by statute, informs Puerto Rico retaliation law. The elements at the prima facie stage (protected activity, adverse action, and causation) were partly undisputed: Román’s reporting to the Fund is protected, and termination is adverse. The controversy centered on causation and pretext.

On causation, the district court collapsed the inquiry into temporal proximity and, viewing a five-month gap as too long, concluded Román failed as a matter of law. The First Circuit found this legally erroneous. Temporal proximity is a permissible—but not required—means of demonstrating causation. Plaintiffs may instead rely on a constellation of circumstantial evidence that, taken as a whole, permits a reasonable inference that the protected activity was a but-for cause of the adverse decision. The opinion expressly warns that if courts or employers treated timing as dispositive, employers could insulate retaliatory actions by waiting out an arbitrary time period, undermining statutory protections.

Proceeding to pretext, the court accepted that Cape Air articulated facially legitimate reasons: uncertainty about Román’s return date and operational need for a third agent. But the analysis did not end there; the question is whether a reasonable jury could find these reasons unworthy of credence given the record. Two sets of inconsistencies did the heavy lifting:

Termination letter vs. litigation rationale: The letter states Román “failed to keep [Cape Air] informed of [his] status” and then announces his termination, which a reasonable factfinder could understand as causally linked. In litigation, Cape Air emphasized “operational needs” and coverage, reasons not mentioned in the letter. The divergence supports an inference of shifting rationales.
Timing contradictions: Cape Air asserted it decided to terminate in May after unread supervisor messages; yet deposition testimony suggests discussions to terminate began in late February (when FMLA leave was expiring), with a decision by April. This discrepancy invites a jury to doubt the company’s proffered sequence and rationale.

Because these inconsistencies could support findings of both pretext and causation, and because summary judgment forbids credibility weighing, the panel concluded a jury must resolve the dispute. The court also clarified that the plaintiff’s failure to appeal the dismissal of his Law 80 wrongful discharge claim does not bar his Law 115 retaliation claim; the two claims are legally distinct and may rise or fall independently.

Impact and Practical Implications

Mercado carries meaningful practical and doctrinal consequences for employment litigation in Puerto Rico and in First Circuit courts applying Puerto Rico law:

No per se temporal-proximity rule: A non-“very close” timing gap (e.g., four to five months) does not doom a retaliation claim where other evidence reasonably links the protected activity to the adverse action. District courts must consider the full record and not truncate causation analysis to the calendar alone.
Shifting explanations are potent evidence: Differences between the contemporaneous termination documentation and later litigation positions can create triable issues on pretext and causation. Employers should ensure contemporaneous records accurately and completely state the reasons for termination.
Summary judgment discipline: Mercado reiterates that courts cannot weigh credibility, resolve disputed inferences, or demand a plaintiff prove retaliation at the summary judgment stage. Showing a genuine factual dispute suffices to reach a jury.
Law 115’s breadth reaffirmed: Reporting to the Puerto Rico State Insurance Fund is a protected activity under Law 115, consistent with Puerto Rico Supreme Court authority. Employer conduct surrounding workplace injuries and Fund filings will be scrutinized.
FMLA and operations are not absolute shields: Legitimate business needs and expired FMLA leave can be real, but if they are invoked inconsistently or as a post hoc justification, they may not defeat a retaliation claim at summary judgment.
Risk of “waiting out” the clock: The court’s admonition cuts against employer strategies that delay adverse actions simply to weaken temporal proximity. Such delays do not immunize a decision from a retaliation claim.

Complex Concepts Simplified

Law 115 (P.R. Laws Ann. tit. 29 § 194 et seq.): Puerto Rico’s whistleblower statute. It forbids retaliation against employees who provide information to legislative, administrative, or judicial forums in Puerto Rico. Seeking benefits or treatment with the State Insurance Fund qualifies.
Protected activity: Conduct the statute protects from retaliation—here, reporting to and receiving treatment from the Puerto Rico State Insurance Fund.
Temporal proximity: How close in time the protected activity is to the adverse action (like termination). While important, it is not the only way to show causation.
Prima facie case: The plaintiff’s initial, relatively light burden to show protected activity, adverse action, and a causal link between the two.
Burden shifting (McDonnell Douglas): After a prima facie showing, the employer must articulate a legitimate, non-retaliatory reason for its action; then the burden shifts back to the plaintiff to show that reason is a pretext.
Pretext: A false or contrived explanation offered to mask retaliatory motive. Evidence includes inconsistencies, contradictions, or changing reasons.
But-for causation: The idea that the adverse action would not have occurred absent the retaliatory motive. Showing pretext often supports a but-for inference.
Summary judgment: A procedural device to resolve cases without trial when there is no genuine dispute of material fact. Courts must view the record in favor of the nonmovant and cannot weigh credibility.
State Insurance Fund (the Fund): Puerto Rico’s workers’ compensation system. Employers’ handling of Fund-related reporting and treatment can be materially relevant in Law 115 cases.
Law 80 vs. Law 115: Law 80 addresses wrongful discharge without just cause; Law 115 addresses retaliation. A failure on one does not automatically defeat the other.

Practical Guidance for Employers and Litigants

Document consistently: Termination letters should accurately and comprehensively state the reasons for separation. Later “operational” rationales that do not appear in the contemporaneous record invite pretext findings.
Align testimony with documents: Deposition and hearing testimony about when and why a decision was made should match internal emails, notes, and letters. Inconsistencies can be case dispositive at trial.
Do not rely on timing alone: Plaintiffs should compile evidence of employer knowledge of protected activity, planning discussions, deviations from policy or practice, disparate treatment, and shifting explanations to demonstrate causation and pretext.
Avoid retroactive termination dating where possible: Backdating effective dates—especially when an employer knows the employee is under medical restrictions—can appear retaliatory unless well supported and consistently documented.
Train supervisors on Fund processes: Missteps in reporting workplace injuries to the Fund or steering employees toward private insurance can become probative context in retaliation claims.

Conclusion

Mercado v. Hyannis Air Service, Inc. clarifies, with precedential force in the First Circuit’s Puerto Rico docket, that temporal proximity is not a mandatory ingredient of causation in Law 115 retaliation cases. Courts must consider the entire evidentiary mosaic, including inconsistent or shifting explanations, to determine whether a jury could find that protected activity caused the adverse action. The opinion also reinforces the stringency of summary judgment constraints and reaffirms that evidence of pretext often doubles as evidence of causation. For employers, Mercado underscores the need for clear, consistent, contemporaneous documentation of termination decisions; for employees, it confirms that a time gap alone does not foreclose a retaliation claim when other circumstantial evidence points to retaliatory motive. In short, Mercado meaningfully refines the Law 115 causation analysis and will influence how retaliation claims are pled, defended, and decided in Puerto Rico and in First Circuit courts applying Puerto Rico law.