In 1976, Frank Fitzsimmons, president of the Teamsters, struck a defiant note in a speech at the union’s convention in Las Vegas. “To those who say it is time to reform this organization, and it’s time officers stopped selling out the members,” he said, “I say to them, ‘Go to hell.’ ”

The next day, Pete Camarata, a rank-and-file Teamster dedicated to reform, rose to say he opposed Mr. Fitzsimmons’s re-election as well as a pay raise for him. He said Mr. Fitzsimmons and his lieutenants had stifled democracy in the union and ignored workers’ concerns. He called for a rule that would automatically expel any Teamster officer who accepted a bribe from an employer.

Boos and catcalls drowned out his remarks.

Afterward, Mr. Camarata — who died last Sunday in Chicago at 67 — attended a cocktail party in the hotel ballroom, but felt unwelcome and excused himself. Several beefy sergeants-at-arms offered to escort him outside. (Mr. Camarata himself was a hefty man, at one point weighing 400 pounds.) Suddenly, one of them punched him. Others kicked him in the head with their pointed cowboy boots. His face was left purple and swollen, his right eye closed.

The police were sympathetic, until they conferred with Teamster officials. According to Lester Velie’s 1977 book about the Teamsters leader Jimmy Hoffa, “Desperate Bargain: Why Jimmy Hoffa Had to Die,” one officer then said, “Get out of town, buddy, and get out fast.”

Mr. Camarata left Las Vegas, but he did not abandon his fight to reform the International Brotherhood of Teamsters. In 1981, as head of a dissident group, he ran for president of the union, the first outsider to challenge its leadership. He lost badly.

The campaign was one of many fights his group, Teamsters for a Democratic Union, picked with a union that the federal government regarded as corrupt. Some were successful. In 1989, the Teamsters leadership accepted the group’s proposals for electoral reform. By agreeing to the direct election of international officers, the union avoided a federal trial on racketeering charges but was subjected to government supervision.

The dissident group grew to more than 8,000 members, and though it comprised just a tiny fraction of the union’s total membership of two million, it was a major force in the election of Ron Carey as a reform candidate for Teamsters president in 1991. Mr. Carey included group members in his leadership coalition. (He was later forced out by the federal government, accused of receiving illegal campaign contributions.)

Mr. Camarata retired from the work force in 1995 but continued to fight for union reforms until his death of renal cancer, his wife, Robin Potter, said.

His first marriage ended in divorce. Besides his wife, he is survived by a stepdaughter, Aimee Potter, and a stepson, Jackson Potter.

Peter Joseph Camarata was born in Detroit on Sept. 7, 1946. His father, Caspar, worked at the Packard Motor Car Company for 36 years, where he helped the United Automobile Workers organize. His mother, Mary, cooked in restaurants and at union meetings.

Pete attended Roman Catholic schools and sang in a choir. As a high school student he helped collect day-old bread for a shelter for the homeless. He enrolled at Wayne State University in Detroit and got a job on the loading dock of a trucking company to help with expenses. He ended up dropping out to work full time on the dock and began to think of himself more as a Teamster than as a worker. He became active in Local 299 — the local of both Mr. Hoffa and Mr. Fitzsimmons — and was elected steward.

He was a Hoffa ally. After Mr. Hoffa was released from prison in 1971 — pardoned by President Richard M. Nixon after serving time since 1967 on jury-tampering and fraud charges — Mr. Camarata worked unsuccessfully for his return to the union.

Mr. Fitzsimmons was acting president during Mr. Hoffa’s imprisonment and became president in 1971 when the pardon barred Mr. Hoffa from further union activity. Mr. Hoffa disappeared in Detroit in 1975 and was declared dead in 1982.

At Local 299, Mr. Camarata joined with other young leftist Teamsters to press for more local autonomy. They became affiliated with an organization on college campuses called International Socialists.

In 1976, to win a better contract in Detroit, Mr. Camarata helped lead a wildcat strike in which 300 Teamsters managed to cripple the city. “There wasn’t a truck that moved,” he said in “Detroit Lives,” a 1994 book compiled and edited by Robert H. Mast. “The union bureaucrats were against us, and we had to fight them, too.”

One result of the strike was his election as a delegate to the national convention in Las Vegas. After his open defiance there, he was expelled from the union twice but successfully fought to be reinstated both times. He told Mr. Mast that he had been threatened physically many times.

A flier, signed by a Local 299 member, alleged that the dissident group was financed by illegal drug trafficking. The group denied this. The flier also referred to Mr. Camarata’s weight, explaining his rise to leadership with the phrase “Fat floats.” (He eventually lost 200 pounds and was featured in weight-loss publications, his wife said.)

When Mr. Fitzsimmons consigned Mr. Camarata and other dissidents to hell in 1976, Mr. Camarata had a ready reply: “We’ll meet him wherever he wants.”