LOS ANGELES (AP) — Tens of thousands of academic employees across the University of California’s 10 campuses walked off the job Monday, demanding better pay and benefits in what union leaders say could be the largest work stoppage the prestigious public university system has ever faced.

The unions representing some 48,000 teaching assistants, researchers, postdoctoral scholars, tutors and graders say the vast majority of members turned out at picket lines starting at 8 a.m. They say they are seeking significant pay increases and child-care subsidies to afford the cost of living in cities such as Los Angeles, San Diego and Berkeley, where housing costs are soaring.

The strike threatens to disrupt classroom and laboratory instruction across the statewide university system just weeks ahead of final exams in December. Some instructors were already telling some students classes were on hold indefinitely.

Organizers from the United Auto Workers, which represents the employees involved, say they have set no end date for the work stoppage.

“The strike will end when UC ends its unfair labor practices and starts bargaining in good faith,” said Neal Sweeney, president of the UAW Local 5810, representing about 12,000 UC postdoctoral and academic researchers.

He said the unionized workers, represented by four bargaining units, are seeking pay that will lift workers out of “rent burden,” which is defined by the federal government as having to pay at least a third of your salary toward rent.

The average current pay is about $24,000 annually for student employees including teaching assistants and tutors who “collectively do the majority of instruction,” at UC schools, he said.

They are seeking minimum annual base salaries of $54,000.

UC has offered a salary scale increase of 5% in the first year and 3% afterward, but workers say that is not adequate.

In a statement, UC said it had entered the talks with a “genuine willingness to compromise,” adding that “many tentative agreements” on issues such as health and safety had been reached.

“UC’s primary goal in these negotiations is multiyear agreements that recognize these employees’ important and highly valued contributions to UC’s teaching and research mission with fair pay, quality health and family-friendly benefits, and a supportive and respectful work environment,” the statement said.

Ally Cara, 32, a postdoctoral researcher in endocrinology at the University of California Los Angeles, spends half of her income on rent, paying $2,000 for a one-bedroom apartment.

“Most of us are severely rent burdened and some of us are having to choose between paying rent and buying groceries and medication,” said Cara, who moved from Michigan and has been in Los Angeles just over a year. Rents are increasing everywhere but she said “California is uniquely higher.”

According to the UAW, the strike is the largest to occur at the University of California and could be the largest academic strike in higher education in U.S. history.

James Boocock, a postdoctoral scholar in human genetics at UCLA, joined one of six pickets on campus. He said striking “was a tough decision to make” given he loves his research but added salaries are unsustainable and the university doesn’t provide enough support.

Besides pay raises, the unionized workers are demanding child care subsidies, enhanced health care for dependents, public transit passes, lower tuition costs for international scholars and greater accessibility for workers with disabilities.

Demonstrators were out in force at UC campuses in Los Angeles and Berkeley, Santa Cruz, Merced, Santa Barbara, and Irvine. Some 300,000 students attend the 10 schools that make up the University of California. On some campuses, students joined in solidarity.

Lex Von Klark, a 22-year-old political science student at UCLA, was among several hundred people on campus holding signs and participating in picket lines Monday.

“I am out here primarily because these people are my teachers, and their working conditions are my learning conditions,” he said. “Basically if my teachers are getting paid less than a living wage and have to work multiple jobs, it makes it hard for me to get a high-end education.”

A group of 33 state lawmakers sent a letter last week to UC President Michael Drake in support of the student employees.

“The UC is one of the top public university systems and research institutions in the world, in no small part because of its ability to attract the most talented scholars from a wide array of backgrounds, the letter said. “But the UC system cannot live up to its mission and reputation if its own employees do not feel respected.”

The lawmakers urged the university to bargain in good faith with the workers: “By failing to do so, UC is risking mass disruption and losing the talent that has earned UC its prestigious reputation.”