29 C.F.R. § 1620.16 : Labor — REGULATIONS RELATING TO LABOR — EQUAL EMPLOYMENT OPPORTUNITY COMMISSION — THE EQUAL PAY ACT — Jobs requiring equal effort in performance

(a) In general. The jobs to which the equal pay standard is applicable are jobs that require equal effort to perform. Where substantial differences exist in the amount or degree of effort required to be expended in the performance of jobs, the equal pay standard cannot apply even though the jobs may be equal in all other respects. Effort is concerned with the measurement of the physical or mental exertion needed for the performance of a job. Job factors which cause mental fatigue and stress, as well as those which alleviate fatigue, are to be considered in determining the effort required by the job. "Effort" encompasses the total requirements of a job. Where jobs are otherwise equal under the EPA, and there is no substantial difference in the amount or degree of effort which must be expended in performing the jobs under comparison, the jobs may require equal effort in their performance even though the effort may be exerted in different ways on the two jobs. Differences only in the kind of effort required to be expended in such a situation will not justify wage differentials.
(b) Comparing effort requirements of jobs. To illustrate the principle of equal effort exerted in different ways, suppose that a male checker employed by a supermarket is required to spend part of his time carrying out heavy packages or replacing stock involving the lifting of heavy items whereas a female checker is required to devote an equal degree of effort during a similar portion of her time to performing fill-in work requiring greater dexterity-such as rearranging displays of spices or other small items. The difference in kind of effort required of the employees does not appear to make their efforts unequal in any respect which would justify a wage differential, where such differences in kind of effort expended to perform the job are not ordinarily considered a factor in setting wage levels. Further, the occasional or sporadic performance of an activity which may require extra physical or mental exertion is not alone sufficient to justify a finding of unequal effort. Suppose, however, that men and women are working side by side on a line assembling parts. Suppose further that one of the men who performs the operations at the end of the line must also lift the assembly, as he completes his part of it, and places it on a waiting pallet. In such a situation, a wage rate differential might be justified for the person (but only for the person) who is required to expend the extra effort in the performance of his job, provided that the extra effort so expended is substantial and is performed over a considerable portion of the work cycle. In general, a wage rate differential based on differences in the degree or amount of effort required for performance of jobs must be applied uniformly to men and women. For example, if all women and some men performing a particular type of job never perform heavy lifting, but some men do, payment of a higher wage rate to all of the men would constitute a prohibited wage rate differential if the equal pay provisions otherwise apply.

29 C.F.R. § 1620.16