Hoffa was involved with the International Brotherhood of Teamsters union, as an organizer from 1932 to 1975. He served as the union's General President from 1958 to 1971. He secured the first national agreement for teamsters' rates in 1964, and played a major role in the growth and development of the union, which eventually became the largest single union in the United States, with over 1.5 million members during his terms as its leader.
Hoffa, who had been convicted of jury tampering, attempted bribery, and fraud in 1964, was imprisoned in 1967, sentenced to 13 years, after exhausting the appeal process. However, he did not officially resign the Teamsters' presidency until mid-1971. This was part of a pardon agreement with U.S. president Richard Nixon, in order to facilitate Hoffa's release from prison in late 1971. Nixon blocked Hoffa from union activities until 1980; Hoffa was attempting to overturn this order and to regain support. He was last seen in late July 1975, outside a suburban Detroit restaurant called the Machus Red Fox.