A strike by graduate student workers has spread to six campuses across the University of California system, as administrators now turn to the courts in an effort to force the strikers back to work.

The work stoppage appears to be the largest so far this year in the U.S, involving a majority of the 48,000 academic workers who are members of the United Auto Workers Local 4811. The union organized the strike last month in response to the universitys crackdown on pro-Palestinian protests and encampments stemming from Israels military campaign in Gaza.

The latest school to take part in the strike was UC Irvine, where grad students walked off the job on Wednesday morning, according to Local 4811. They were preceded by grad students at UC Santa Barbara and UC San Diego, who joined the strike on Monday, and UC Davis, UCLA and UC Santa Cruz, who walked off in May.

In total, the union has called on 31,500 members in the system to stop working, although exactly how many have hit the picket lines is unclear. Seventy-nine percent of members were in favor of authorizing the strike when a vote was held in mid-May, the union said. (Earlier this year, up to 29,000 faculty members at California State University went on a one-day strike in a contract dispute .)

Tanzil Chowdhury, a graduate student instructor and executive board member of the union, said members across the UC system were agitated over the universitys handling of protests. Police made more than 200 arrests at UCLA after counterprotesters violently attacked pro-Palestinian demonstrators, and dozens more later at UC Irvine. The university said it believed the encampments posed a public safety threat.

A huge number of our workers are extremely unhappy with the way that the university has been conducting itself, said Chowdhury, a Ph.D. student in the materials science and engineering program at UC Berkeley. People really understand the grave threat that the university is posing to us.

The university has twice sought to have a state labor relations board force the grad students back to work , arguing that the work stoppage was illegal and causing irreparable harm. Their requests that the board seek an injunction in court were denied both times.

On Tuesday, the university took their fight to state court, filing a lawsuit in Orange County seeking a temporary restraining order to end the strike. The suit claims the work stoppage violates the no-strike clause in the unions contract, and alleges some picketers have blocked entrances at schools and hospitals and barricades themselves in campus buildings.