29 C.F.R. § 825.303 : Labor — REGULATIONS RELATING TO LABOR — WAGE AND HOUR DIVISION, DEPARTMENT OF LABOR — OTHER LAWS — THE FAMILY AND MEDICAL LEAVE ACT OF 1993 — EMPLOYEE AND EMPLOYER RIGHTS AND OBLIGATIONS UNDER THE ACT — Employee notice requirements for unforeseeable FMLA leave

(a) Timing of notice. When the approximate timing of the need for leave is not foreseeable, an employee must provide notice to the employer as soon as practicable under the facts and circumstances of the particular case. It generally should be practicable for the employee to provide notice of leave that is unforeseeable within the time prescribed by the employer's usual and customary notice requirements applicable to such leave. See§ 825.303. Notice may be given by the employee's spokesperson ( e.g., spouse, adult family member, or other responsible party) if the employee is unable to do so personally. For example, if an employee's child has a severe asthma attack and the employee takes the child to the emergency room, the employee would not be required to leave his or her child in order to report the absence while the child is receiving emergency treatment. However, if the child's asthma attack required only the use of an inhaler at home followed by a period of rest, the employee would be expected to call the employer promptly after ensuring the child has used the inhaler.
(b) Content of notice. An employee shall provide sufficient information for an employer to reasonably determine whether the FMLA may apply to the leave request. Depending on the situation, such information may include that a condition renders the employee unable to perform the functions of the job; that the employee is pregnant or has been hospitalized overnight; whether the employee or the employee's family member is under the continuing care of a health care provider; if the leave is due to a qualifying exigency, that a military member is on covered active duty or call to covered active duty status (or has been notified of an impending call or order to covered active duty), that the requested leave is for one of the reasons listed in §825.126(b), and the anticipated duration of the absence; or if the leave is for a family member that the condition renders the family member unable to perform daily activities or that the family member is a covered servicemember with a serious injury or illness; and the anticipated duration of the absence, if known. When an employee seeks leave for the first time for a FMLA-qualifying reason, the employee need not expressly assert rights under the FMLA or even mention the FMLA. When an employee seeks leave due to a qualifying reason, for which the employer has previously provided the employee FMLA-protected leave, the employee must specifically reference either the qualifying reason for leave or the need for FMLA leave. Calling in "sick" without providing more information will not be considered sufficient notice to trigger an employer's obligations under the Act. The employer will be expected to obtain any additional required information through informal means. An employee has an obligation to respond to an employer's questions designed to determine whether an absence is potentially FMLA-qualifying. Failure to respond to reasonable employer inquiries regarding the leave request may result in denial of FMLA protection if the employer is unable to determine whether the leave is FMLA-qualifying.
(c) Complying with employer policy. When the need for leave is not foreseeable, an employee must comply with the employer's usual and customary notice and procedural requirements for requesting leave, absent unusual circumstances. For example, an employer may require employees to call a designated number or a specific individual to request leave. However, if an employee requires emergency medical treatment, he or she would not be required to follow the call-in procedure until his or her condition is stabilized and he or she has access to, and is able to use, a phone. Similarly, in the case of an emergency requiring leave because of a FMLA-qualifying reason, written advance notice pursuant to an employer's internal rules and procedures may not be required when FMLA leave is involved. If an employee does not comply with the employer's usual notice and procedural requirements, and no unusual circumstances justify the failure to comply, FMLA-protected leave may be delayed or denied.

29 C.F.R. § 825.303