Start the citation with “United States” followed by a period, followed by “Cong.” Include whether it is Senate or House of Representatives.
List the name of the bill in italics, followed by a period.
List the number and session of Congress, abbreviating the word “Congress” to “Cong.”
List the bill number such as “S 33” or “HR 77” followed by a period.
List the publication where it is found with place, publisher, date and medium of publication. Government documents are usually printed by the Government Printing Office, which you can cite as “GPO.” Your completed citation might look like this:
“United States. Cong. Senate. Military Registration and Mobilization Assessment Act of 1979. 96th Cong., 1st sess. S 226. Washington: GPO, 1979. Print."