seniority

In providing that a veteran shall be restored to the position he had before he entered the military service 'without loss of seniority,' § 8 of the Act uses the term 'seniority' without definition. It is thus apparent that Congress was not creating a system of seniority but recognizing its operation as part of the process of collective bargaining. We must therefore look to the conventional uses of the seniority system in the process of collective bargaining in order to determine the rights of seniority which the Selective Service Act guaranteed the veteran. Barring legislation not here involved, seniority rights derive their scope and significance from union contracts, confined as they almost exclusively are to unionized industry.