The transit union’s 34,000 members will likely authorize a strike when they gather at the Jacob K. Javits Convention Center on Saturday, but the decision to walk off the job could ultimately be on one man’s shoulders: the union’s president, Roger Toussaint.

Mr. Toussaint, 49, is considered by those familiar with the inner workings of the union to be a tough, smart, and practical man who is steeped in grassroots activism and sees the interests of his members aligned with those of riders.

Although he was elected president in 2000 based on his reputation as a radical – and has led two small bus strikes in five years – he has shown the ability to broker deals while maintaining the support of the rank and file and, perhaps more importantly, the executive board ultimately responsible for voting to strike.

According to his official biography published by the union, he was expelled from school in his native Trinidad when he was 17 for writing slogans on the walls. One read: “Free education means free books.” He came to New York in 1974.

Soon after he was hired as a track worker in 1984, he began publishing a newsletter with other workers that called attention to grievances over work conditions. In 1994, he was elected to a union position in charge of 1,800 members.

Mr. Toussaint was fired in 1998 for allegedly working on union business while he was supposed to be working for the MTA. He filed a successful lawsuit, and during court proceedings it was disclosed that the transit authority had spent $10,000 to have Mr. Toussaint trailed.

The controversy catapulted Mr. Toussaint into the hearts and minds of the rank and file.

“He was a hero throughout the local as someone who was able to fight back,” a member of the executive board, Marty Goodman, said.

One of his first moves after he was elected was to cut his salary by 25%.

Mr. Goodman said he believes Mr. Toussaint has since betrayed that reputation. He cited the 2002 contract for subway and bus workers that resulted in a pay freeze the first year, except for a $1,000 bonus, and the loss of a clause that protected workers from layoffs.

“He promised never to accept zero,” Mr. Goodman said. “And here he built his reputation on being a militant.”

Mr. Goodman said he plans to protest Mr. Toussaint’s handling of the negotiations on Saturday.

The last subway strike occurred in 1980, after the executive board overrode the wishes of the union president at the time, John Lawe, to accept the contract he had negotiated, according to labor historian Joshua Freeman, a professor at the City University of New York Graduate Center.

By contrast, Mr. Freeman said: “Roger is obviously a very forceful guy. He speaks his mind. He doesn’t suffer fools gladly.” And so any strike decision will have to go through him.