We look first to legal efforts to exclude persons conceived to be subversive from private employment, and then survey the statutes governing public employment. The Defense Production Act of June 21, 1940,[242] for example, imposed the rule that aliens working for a defense contractor whose contract involved access to classified information were ineligible to work for the contractor. If, however, the head of the government agency for whom secret work was being performed gave the contractor written consent to use aliens, the contractor was free to do so. Attempting to insure that employment opportunities created by the induction of young men into the service did not accrue to members of groups then opposing the American defense effort, Congress, in enacting the Selective Training and Service Act of 1940, stipulated that whenever a vacancy was caused in the employment rolls of any business or industry by reason of an employee’s induction into the Armed Services of the United States, the vacancy could not be filled by any person then a member of the Communist Party or the German-American Bund.[243] Ten days after Pearl Harbor, restraints were placed on the liberty of maritime employers to hire radio operators for service on American flag vessels. For the duration of war emergency it became unlawful to employ any person to serve as radio operator aboard any vessel (other than a vessel of foreign registry) if the Secretary of the Navy (1) had disapproved such employment for any specified voyage, route, or area of operation, and (2) had notified the master of the vessel of such disapproval prior to the vessel’s departure.[244] Since the war, no less significant prohibitions have been placed on public or private employment of members of communist organizations. The effect thereof will be determined by the success of the Subversive Activities Control Board in compelling the registration of such groups. Section 5 of the Internal Security Act of 1950 makes it illegal for members of registered communist organizations to conceal or fail to disclose such membership in seeking or accepting any employment in any defense facility, as defined and listed by the Secretary of Defense. This provision was extended to make illegal defense employment for members of registered “Communist action” groups.[245]