29 CFR § 785.32 - Apprenticeship training.
As an enforcement policy, time spent in an organized program of related, supplemental instruction by employees working under bona fide apprenticeship programs may be excluded from working time if the following criteria are met:
(a) The apprentice is employed under a written apprenticeship agreement or program which substantially meets the fundamental standards of the Bureau of Apprenticeship and Training of the U.S. Department of Labor; and
(b) Such time does not involve productive work or performance of the apprentice's regular duties. If the above criteria are met the time spent in such related supplemental training shall not be counted as hours worked unless the written agreement specifically provides that it is hours worked. The mere payment or agreement to pay for time spent in related instruction does not constitute an agreement that such time is hours worked.