Roger Toussaint’s role in his union’s illegal transit strike in December is going to cost him 10 days in jail.

Well-coiffed and dressed in a black suit with a bright lime-green tie, the president of Local 100 of the Transport Workers Union yesterday pleaded guilty to contempt of court charges, as did the union’s secretary-treasurer, Ed Watt, and recording secretary, Darlyne Lawson. Brooklyn Judge Theodore Jones, who presided over yesterday’s hearing, had ordered the union not to strike, but it went forward with a three-day walkout that paralyzed the city’s public transportation system. Under the state’s Taylor law, it is illegal for public sector unions to strike.

Mr. Watt and Ms. Lawson were each fined $500, while Mr.Toussaint must pay $1,000 and serve the jail time, which the Metropolitan Transportation Authority had backed away from arguing for.

An incredulous grin spread across Mr. Toussaint’s face when Judge Jones delivered his ruling. The sentence will start in one month.

Judge Jones was terse in his ruling, saying that he found the struggle between the MTA and the TWU to be a troubling chapter in the city’s labor history.

“I am confounded by the tortured tale of these negotiations,” he said. “It is unfortunate that it has to come down to this.”

Mr. Toussaint wore a yellow “Vote Yes” pin, a reminder of the different paths the MTA and the union have taken since the strike ended more than three months ago. Although its contract expired on December 16, the union is still without a bargaining agreement with the MTA. The union last week sent out ballots for a second vote on the original contract agreement reached at the end of the strike, which its membership voted down in January by seven votes. The MTA has said it will not accept a revote on the contract and will only accept a contract imposed by a state arbitration panel. The Public Employee Relations Board has already begun this process.

After brief statements from lawyers for each side, Mr. Toussaint addressed the judge in a statement, admitting to being in contempt of court. He characterized the strike as the union’s last option in dealing with an unjust employer.

“As a matter of practice and common sense, a strike was a last resort,” he said. “We did it because we felt we had to.”

He blamed the MTA for pushing the union into a strike, calling its behavior during negotiations “cavalier and provocative.” He said the Taylor law was “illegal” and argued that it gave the employer an unfair hand in negotiations by allowing it to hold out on reaching a contract for months or years.

During his arguments against Mr. Toussaint and the other officers, an MTA lawyer, James Henly, said the court should make sure its punishment “sends a very strong signal that future illegal strikes endangering the public will not be tolerated.”

A number of Brooklyn politicians, including Assemblyman Nick Perry, a Democrat of Brooklyn who is running for Congress, said Mr. Toussaint was a hero and that the jail sentence would make him a martyr. Echoing Mr. Toussaint’s statements during the court proceedings, Mr. Perry said he would introduce legislation in Albany to change the “flawed” Taylor Law.

The chairman of the MTA board, Peter Kalikow, said in a statement last night that he felt the decision “reflects the gravity of the union’s decision to knowingly and willfully violate the law.”

The union hasn’t yet decided whether it will appeal the decision, a union source said.

Asked if he regretted his decision to go on strike, Mr. Toussaint said he was well prepared for the day he would be sent to jail for his role in the walkout.

The mother of Matt Long, the firefighter who was hit by a bus while riding his bicycle during the strike, said the sentence was “partial justice.”

“I don’t think 10 days is enough really because my son has been in the hospital for 100 days,” Eileen Long said.

Mr. Jones postponed discussion of whether the union should pay $3 million in fines for breaking the Taylor law. When the strike was authorized, Mr. Jones ruled in December that every day the union was on strike, it would be penalized $1 million on top of the individual fines against striking employees. At a hearing on Friday, a union lawyer, Arthur Schwartz, said Local 100 would have to shut down its office if it was forced to pay that total. He argued that the Taylor law was not intended to bankrupt unions.