LOS ANGELES (Reuters) – More than 30,000 Los Angeles teachers demanding higher pay and smaller class sizes walked off the job in America’s second-largest school system on Monday, marching in the rain after negotiations over a new contract broke down.

Students arriving for classes at some 900 campuses across the Los Angeles Unified School District were met by their teachers carrying picket signs and rallying for higher salaries, increased staff and smaller classes in the city’s first teachers’ strike in three decades. The system educates some 640,000 students.

“It’s an existential battle for the future of public education,” teacher Mike Finn told Reuters outside John Marshall High School in the Los Angeles neighborhood of Los Feliz.

Thousands of teachers and supporters gathered outside City Hall, carrying umbrellas in the rain and chanting as they prepared to march toward district headquarters.

The walkout marks the latest in a wave of teachers’ strikes across the United States over pay and other school issues, following job actions in West Virginia, Kentucky, Oklahoma and Arizona.

Some teachers in Denver also walked out on Monday amid salary negotiations, according to a video posted on the Denver Classroom Teachers Association’s Twitter page.

But the strike by United Teachers Los Angeles (UTLA) marks one of the largest and one of the few targeting a Democratic-controlled government. Los Angeles County officials contend the strikers’ demands are unaffordable and that a walkout hurts only students and parents.

Los Angeles Mayor Eric Garcetti, a Democrat who has said he is considering a run for his party’s nomination in the 2020 presidential race, has largely avoided taking sides in the labor dispute.

In a video posted to Twitter on Sunday evening, Garcetti urged the district and union to reach an agreement as soon as possible. In a separate tweet, he said the city was offering free rides to students on transit systems.

Union negotiators have demanded a 6.5 percent pay raise, more librarians, counselors and nurses on campuses, smaller class sizes and less testing, as well as a moratorium on new charter schools.

The district has countered with a proposed 6 percent salary hike with back pay and a $100 million investment to hire more staff and decrease class sizes.

Talks broke down on Friday evening with union leaders saying they were “insulted” by the latest offer from district officials. The two sides did not meet over the weekend.

Los Angeles County School Superintendent Austin Beutner said Friday’s offer to teachers was beefed up after newly-installed California Governor Gavin Newsom increased education spending in his proposed budget.

County officials have said UTLA’s demands would bankrupt the district.

“Our commitment to our families is to make sure all of the money we have is being spent in schools. We are doing that,” Beutner said in a statement on Friday. “We hope UTLA leadership will reconsider its demands, which it knows Los Angeles Unified cannot meet.”

Nearly a year ago, West Virginia teachers picketed for more than a week before lawmakers officials approved a 5 percent pay raise for all state workers.

In April 2018, Oklahoma teachers ended a nearly two-week strike after securing pay raises and increased education spending. In Kentucky and Arizona, teachers won a boost in funding and wages last year after walkouts.