Under  29 U.S.C. § 141-197 of 1947, better known as the Taft-Hartley Act, the president can impose an 80 day cooling-off period prior to a contract expiring. After expiration, there is no "cooling off." In cases deemed to be National Emergencies, the President can directly intervene in a strike. Presidents since Truman have been rather reluctant to invoke the provisions of the Act.