Correction: An earlier version of this article incorrectly said that Cleveland Mayor Frank Jackson wants to disregard seniority when it comes to firing. Jackson wants to consider other factors in addition to seniority when making firing decisions; under current Ohio law, seniority is the only factor that can be considered. This version has been corrected.

Teachers, staff members, union officials and others wait to speak at a hearing at the Board of Education at Los Angeles Unified School District headquarters, where the board would determine cuts to the budget, in Los Angeles on March 13. (Reed Saxon/AP)

As a young labor organizer in Los Angeles, Antonio Villaraigosa worked for the city’s teachers, honing his political skills in the fight for a good contract. The union loved him back, supporting the Democrat’s election to the State Assembly, City Council and, finally, the mayor’s office he occupies today.

But now, Villaraigosa, a rising star in the national Democratic Party, has a different view. He calls the teachers union “the one, unwavering roadblock” to improving public education in Los Angeles.

Villaraigosa is one of several Democratic mayors in cities across the country — Chicago, Cleveland, Newark and Boston, among them — who are challenging teachers unions in ways that seemed inconceivable just a decade ago.

“This is a very, very interesting political situation that is way counterintuitive,” said Charles Taylor Kerchner, who has written two books about teachers unions.

At at time when most Americans believe that U.S. education is imperiled, and cities are especially struggling to improve schools, the tension between the mayors and the unions is causing a fundamental realignment of two powerful forces in urban politics.

In the clash over what is best for children, adults on both sides are gambling.

The mayors risk turning labor friends into enemies, a lesson then-D.C. Mayor Adrian Fenty learned in 2010 when he lost his seat in part because teachers were enraged by his school reforms. The unions, meanwhile, risk appearing recalcitrant and self-serving, further alienating a public frustrated by failing schools and growing cool to organized labor.

The mayors want a raft of changes. They want to replace the uniform pay scale with merit pay. They seek to expand public charter schools, which are largely non-union. Some want to lengthen school days, requiring teachers to work more hours.

And nearly all of those mayors have set their sights on the one workplace protection that teachers have held central for more than 100 years: tenure.

The unions say many of the “fixes” embraced by the mayors are trendy ideas without evidence that they help children learn. Instead, they allow politicians to appear as if they are making improvements without having to confront the profound problems of urban schools, labor leaders say.

“We don’t want to have honest conversations about poverty and segregation and race and class, all those other sorts of ills,” said Karen Lewis, president of the Chicago Teachers Union. “Those are really tough issues. So this gives them an excuse to focus on something else.”

Her union fought Mayor Rahm Emanuel’s effort to add 90 minutes to the school day in Chicago, which has the shortest school day of any major city. Emanuel, the former chief of staff to President Obama, got the Illinois legislature to pass a law that will allow him to impose a longer school day starting in September. It also makes it harder for the union to strike, among other things.

On the national level, teachers unions have started to recalibrate, looking for ways to work in partnership with politicians.

Randi Weingarten, president of the American Federation of Teachers, acknowledged that the unions have been too focused on fairness for their members and not necessarily quality in the schools.

“We have made mistakes,” she said. “You have to really focus to make sure you’re doing everything you can so that kids are first. Tenure, for example: Make sure tenure is about fairness and make sure it’s not a shield for incompetence.”

First awarded in the 1920s to protect female teachers who could be summarily fired for getting pregnant or marrying, tenure is considered by teachers to be their main protection against firing for political or personal reasons.

But today, tenure makes it nearly impossible to get rid of weak teachers, the mayors say.

“We know how difficult it is to fire a doctor in most of our states — it is significantly more difficult to fire a teacher,” said Villaraigosa, adding that the dismissal rate in Los Angeles is less than 1 percent and 97 percent of the teachers get tenure after two years. “Our current tenure practice is meaningless, so we are challenging it.”

The tough talk coming from Democrats has angered many teachers, who already feel under assault from Republicans. “Teacher unions feel extraordinarily betrayed across this country,” said Lewis of the Chicago Teachers Union.

Many of the mayors are emboldened by reforms promoted by the Obama administration, private philanthropies such as the Bill and Melinda Gates Foundation and organizations such as Democrats for Education Reform, a national political action committee and advocacy group.

“All of us, in one way or another are swimming in their wake,” Emanuel said, referring to President Obama and Education Secretary Arne Duncan.

The mayors say the economic health of their cities depend on better schools.

“Long-term prosperity depends on the ability to keep middle-class families — black, white, Latino — in the city,” said Ed Rendell, a Democrat who served as Philadelphia mayor and Pennsylvania governor. “There’s a growing understanding among the mayors that, in some ways, it’s the whole ball of wax.”

In Cleveland, Democratic Mayor Frank Jackson has proposed a sweeping education plan that would reset the relationship between the city and its teachers.

Jackson wants to consider other factors in addition to seniority when making firing decisions; under current Ohio law, seniority is the only factor that can be considered. Jackson also is seeking a “fresh start” provision so that future teacher contracts are negotiated from scratch, among other things.

“I don’t think Democrat or Republican, pro-union or anti-union, public school or charter school,” said Jackson, who is in his second term. “I’m going to have a conversation about educating children. When you do that, all those other things don’t matter. ”

“I’m opposed to anything that eliminates collective bargaining,” Jackson said. “But I’m also opposed to collective bargaining standing in the way of educating children.”

David Quolke, president of the Cleveland Teachers Union, said the mayor crafted his plan with input from business leaders but not teachers.

“This isn’t an education plan,” Quolke said. “The message is ‘Let’s fire our way to improving the schools.’ Republican or Democrat, that’s just the wrong way to proceed in terms of school improvement. It makes it worse, in a sense, that he’s got a D next to his name.”

Kasich tried to curtail bargaining rights for government workers but his law was repealed by voters in November after unions waged an expensive campaign against it. Now the Republican governor said he is praying for the Democratic mayor’s proposal in the hope that it could be expanded statewide.

Jackson said he needs to take drastic action to win political support for more funding for the Cleveland school system, which is teetering on the edge of insolvency, faces a $65 million projected deficit and is among the state’s lowest performing school districts. In the past 10 years, city school enrollment has plummeted by 30,000, with students either moving out of the city or into public charter schools.

“I want a longer school year, flexible days, preschool — all that costs money,” said Jackson, who intends to seek a new school tax in November. “The only way we can get a levy is to demonstrate to people that they will be paying for something that’s different.”

Mayors are not only wrestling with immediate budget shortfalls but see a pension crisis looming ahead.

“Almost all the major districts have hidden huge costs in terms of pensions,” said Kenneth Wong, a political scientist at Brown University who studies mayoral control of urban schools. “The mayors are beginning to realize there is no way the current tax base can support current operations and also deal with pension liability. This is a huge factor in why we see mayors getting more involved.”

The two largest teachers unions, the National Education Association and the American Federation of Teachers, are showing some flexibility by supporting some previously untouchable reforms, such as teacher evaluations. And some local unions in cities such as Baltimore; New Haven, Conn.; and Hillsborough County, Fla., have agreed to embrace some reforms.

Locally, the teachers union in Montgomery County has long collaborated with the administration. Teachers and principals work together to evaluate educators, identifying weak teachers who need extra support and dismissing those who cannot improve. The 12-year-old program has been held up by the U.S. Department of Education as a national model for labor-management cooperation.

But so far, they’re the exception.

“The problem is the teachers unions are decentralized, so you’ve got people on the national level saying one thing, but on the local level, the leaders are older, activist teachers who tend not to want much change,” said one former national labor leader who spoke on condition of anonymity in order to speak frankly about another union. “Rather than having a national strategy for improving quality, they’re on the defensive.”

Still, the mayors face some political risks from the unions, which remain heavy Democratic donors on the state and national level.

In addition to Fenty in D.C., Villaraigosa has also felt the wrath of the unions in Los Angeles. His pick for school board was defeated last spring by a candidate backed by the union. The union and the school board both pushed back against the mayor’s attempt to win direct controls of the schools.

Confrontations between teachers and mayors come as the public has grown cool toward teachers unions. In a 2011 Gallup poll, 47 percent of respondents said teachers unions hurt the quality of education, while 26 percent said they helped. That 2-to-1 margin is a new high point since Gallup began asking the question in 1976.

“In education, most people believe they aren’t getting anything anymore,” said Ester Fuchs, an expert in urban politics who teaches at Columbia University and has worked in the Bloomberg administration in New York City. “If teacher unions stand in the way of trying new things, they’re going to be an easy political target.”

Democrats are still more likely to back teachers unions than Republicans and independents, Gallup found.

While most public school teachers belong to a union, just 7 percent of private-sector workers do, making it harder for the public to support pensions, tenure and other benefits they don’t enjoy in their own jobs.

“The teachers unions lost the battle of the op-ed pages,” Kerchner said. “Up until Randi (Weingarten), there hasn’t been a prominent voice making the case that what’s good for teachers is also good for kids is good for America . . . They’ve lost intellectual leadership on the one hand, and on the other hand, they’re engaged in a political blocking game. It’s a legitimate tactic, but not one you can use without cost.”