The Associated Press

NEW YORK — The teachers’ union for the nation’s largest public school system accused the city on Friday of banning political campaign buttons for the first time in decades. It asked a federal court to reverse the policy and declare that the teachers’ free speech rights were violated.

At a news conference, United Federation of Teachers President Randi Weingarten announced that a lawsuit had been filed in U.S. District Court in Manhattan, challenging enforcement of the policy.

“We couldn’t believe it,” said Weingarten, who wore a Barack Obama lapel button that was no larger than a postage stamp.

The American Federation of Teachers, including its UFT delegates, voted over the summer to endorse Obama’s presidential candidacy.

Weingarten said schools Chancellor Joel Klein urged principals more than two weeks ago to enforce a Department of Education policy requiring complete neutrality regarding political candidates.

City lawyer Paul Marks said the city was still evaluating the lawsuit.

“However, we’re confident that when the court has had the opportunity to fully consider this matter, the city’s position will be upheld,” he said.

Last week, some University of Illinois faculty and students, claiming their right to support political candidates was under assault, held an Obama rally on campus.

The rally followed an official school statement that the law barred state workers from political activities on university property. The school later said it never intended to enforce the law.

The Philadelphia-based Foundation for Individual Rights in Education recently sent a letter of protest after the University of Oklahoma directed students, faculty and staff not to use university e-mail to endorse or oppose a candidate.

The group said it also had received complaints about bans on campaign activities at Iowa Western Community College and Fresno Pacific University in California.

In New York, the UFT’s lawsuit included a copy of a letter it received from the schools.

It urged enforcement of a regulation restricting political activity in school buildings, saying it was necessary “in light of the upcoming presidential election.”

The letter said failure to comply with the regulation may result in disciplinary action.

Norman Siegel, a lawyer representing the union, said there have never been complaints from students, teachers or parents about buttons worn during political campaigns.

He said the city would have to prove that the buttons were disruptive to ban them.

The city also said teachers should not distribute political materials in employee mailboxes or put posters and other materials on bulletin boards, according to the UFT.

Weingarten said teachers should have a right to express their political views, just like anyone else.

She said suppressing political expression was sending the wrong educational message.

“Students can only benefit from being exposed to and engaged in a dialogue about current events, civic responsibilities and the political process,” Weingarten said.

The UFT lists a membership of about 200,000, including 74,000 teachers. The city’s public schools have about 1.1 million pupils.