Fitzsimmons was investigated in 1976 for failing to perform his fiduciary duties as a trustee on the Teamsters' Central States Pension Fund, and forced to resign from the board of trustees in 1977. The U.S. Departments of Labor and Justice first began investigating the fund in January 1976. He was subpoenaed by both the U.S. Senate's Committee on Labor and Public Welfare and by the Labor Department, and testified in public and private regarding loans the pension fund made to certain mob-related businesses and the fund's operations. Although the Internal Revenue Service revoked the fund's non-profit status, the penalty was suspended after Fitzsimmons agreed to remove several trustees (which he did in September 1976). Fitzsimmons and Roy Lee Williams, director of the Central Conference of Teamsters, attempted to remain on the board, but were forced out in March 1977.