“ We hold that the Commission has the power to establish qualifications and maximum hours of service, pursuant to the provisions of § 204 of the Motor Carrier Act, for the entire classification of petitioner's drivers and 'mechanics' and it is the existence of that power (rather than the precise terms of the requirements actually established by the Commission in the exercise of that power) that Congress has made the test as to whether or not § 7 of the Fair Labor Standards Act is applicable to these employees. ”

“ The same motor vehicle, operated by the same driver, on 1 or 2 days in a week may be engaged in transporting property in interstate commerce and the rest of the week may be engaged in intrastate commerce. In our opinion if a driver operates a motor vehicle in the transportation of interstate or foreign commerce on any day of a given week, such driver is subject to the weekly maximum herein prescribed. ”

“ On this basis, the injunction against violation of § 7 of the Fair Labor Standards Act may be issued as to those garagemen and laborers who are not 'mechanics' as defined by the Interstate Commerce Commission, and the issue before us is limited to the proper application of such an injunction to such 'mechanics.'
The drivers are full-time drivers of motor vehicles well within the definition of that class of work by the Commission if the work is done in interstate commerce. ”