29 CFR §790.5

1. (a)In the application of the minimum wage and overtime compensation provisions of the Fair Labor Standards Act to activities of employees on or after May 14, 1947, the determination of hours worked is affected by the Portal Act only to the extent stated in section 4(d). This section requires that:
2. (b)The operation of section 4(d) may be illustrated by the common situation of underground miners who spend time in traveling between the portal of the mine and the working face at the beginning and end of each workday. Before enactment of the Portal Act, time thus spent constituted hours worked. Under the law as changed by the Portal Act, if there is a contract between the employer and the miners calling for payment for all or a part of this travel, or if there is a custom or practice to the same effect of the kind described in section 4, the employer is still required to count as hours worked, for purposes of the Fair Labor Standards Act, all of the time spent in the travel which is so made compensable. 32 But if there is no such contract, custom, or practice, such time will be excluded in computing worktime for purposes of the Act. And under the provisions of section 4(c) of the Portal Act, 33 if a contract, custom, or practice of the kind described makes such travel compensable only during the portion of the day before the miners arrive at the working face and not during the portion of the day when they return from the working face to the portal of the mine, the only time spent in such travel which the employer is required to count as hours worked will be the time spent in traveling from the portal to the working face at the beginning of the workday.