LOS ANGELES — Cafeteria workers, bus drivers, and other workers for the Los Angeles Unified School District will go on a three-day strike next week, and their union says tens of thousands of teachers have vowed to not cross picket lines.

The strike at the nation's second-largest school district is scheduled from March 21 through March 23, the Service Employees International Union Local 99 said.

The SEIU said in a statement that the teachers' union, United Teachers Los Angeles, has promised not to cross picket lines. The UTLA represents around 30,000 teachers.

The SEIU wants wage increases, more full-time work and more staffing for student services. In addition to cafeteria workers, bus drivers and custodians, its members are also special education assistants.

The Los Angeles teachers union went on a strike in 2019 that lasted seven days. The strike ended with an agreement for pay raises, promises to reduce class size, and other issues.

The school district has over 600,000 students in kindergarten through 12th grade at over 1,000 schools, it says on its website.

LAUSD Superintendent Alberto M. Carvalho in a statement Wednesday called on the service workers union to come back to the negotiating table.

Carvalho, who was hired in late 2021 and took office in February 2022, said with the teachers' union telling its members to support the SEIU strike, teachers may not be available for classroom instruction.

“SEIU is simply refusing to negotiate,” Carvalho said. He said the district had made a “historic offer” to the union designed to address its demands.

The service workers union says it has been negotiating with the district since April. It says the district over-relies on a low-paid workforce that is part-time.

The average salary of school workers at LAUSD is $25,000 a year and most work part-time hours, SEIU said in the statement.

“Families have been sacrificing for far too long on poverty wages," Max Arias, SEIU Local 99’s Executive Director, said.

The announcement of the strike came on the same day teachers and others rallied in the Grand Park area of downtown Los Angeles, NBC Los Angeles reported.

The school district said Tuesday that it had offered wage increases of 5% for the school year that began in 2022, 5% for the one that begins in 2023, and one-time bonuses of 4% and 5% in 2022-2023 and 2023-2024, respectively.