It may be noted that the Butler Bill of April 1955 would have empowered the President to establish procedures for screening any person in defense employment “as to whom there is reasonable cause to believe may engage in sabotage, espionage, or other subversive acts.” This process of screening also would be applied to firms seeking or holding defense contracts. Thus, increasingly access of private firms to government contracts as well as access of individuals to jobs under such contracts, which today may be the staff of life, is being restricted. Contributing to this trend is the provision in the Rubber Producing Facilities Disposal Act of 1953 that purchase proposals shall not be accepted from any person who has not identified his principal, or is not financially responsible, or is a poor security risk.[246] Freedom of employees to strike defense industries or to engage in so-called emergency strikes has on occasion been severely limited. The War Labor Disputes Act of 1943 required that the government be given notice of labor disputes, and that production continue for a period of thirty days after notice of intention to strike. A secret ballot of employees had to be conducted prior to calling a strike.[247] The President was granted ultimate power to seize plants if necessary to avoid interruption of war production occasioned by labor disputes, and interference with government operation of such plants was made illegal.[248] The plants were to be operated under the terms and conditions of employment which were in effect at the time possession was taken by the government.[249] In the post-war Labor-Management Relations Act a national emergency strike is defined as one imperiling “the national health or safety.”[250] When, in the opinion of the President, a threatened or existing strike or lockout affecting an entire industry or a substantial part thereof imperils the national health or safety, he may appoint a board of inquiry to inquire into the issues involved in the dispute and to make a written report to him within such time as he shall prescribe.[251] When the President has received a report from a board of inquiry, he may direct the Attorney General to petition any district court of the United States having jurisdiction of the parties to enjoin such strike or lockout or its continuance, and if the court finds that a threatened or actual strike or lockout (1) affects an entire industry or a substantial part thereof engaged in trade, commerce, transportation, transmission, or engaged in the production of goods for commerce; and (2) if permitted to occur or to continue, will imperil the national health or safety, it shall have jurisdiction to enjoin any such strike or lockout.[252]