(NewsNation) — Workers in America’s second-largest school district began a three-day walkout Tuesday, shutting down instruction for hundreds of thousands of students in Los Angeles.

Demonstrations began at a bus yard by members of Local 99 of the Service Employees International Union, which represents about 30,000 teachers’ aides, special education assistants, bus drivers, custodians, cafeteria workers and other support staff.

Teachers, cafeteria workers and bus drivers were among the employees walking the picket lines.

Leaders of United Teachers Los Angeles, the union representing 35,000 educators, counselors and other staff, pledged solidarity with the strikers.

“These are the co-workers that are the lowest-paid workers in our schools and we cannot stand idly by as we consistently see them disrespected and mistreated by this district,” UTLA President Cecily Myart-Cruz told a news conference.

Myart-Cruz was joined by U.S. Rep. Adam Schiff, a Democrat and U.S. Senate candidate, who said the strikers were earning “poverty wages.”

“People with some of the most important responsibilities in our schools should not have to live in poverty,” Schiff said.

Last-minute negotiations between Los Angeles Unified School District officials and the Service Employees International United Local 99, or SEIU, were not enough to avert the strike.

Superintendent Alberto M. Carvalho accused the union of refusing to negotiate and said that he was prepared to meet at any time day or night. He said Monday a “golden opportunity” to make progress was lost.

“I believe this strike could have been avoided. But it cannot be avoided without individuals actually speaking to one another,” he said.

The union announced that the strike would begin on Tuesday, March 21, and continue through Thursday, March 23.

Among other goals, SEIU is seeking a 30% pay raise. The district is currently offering about 15%, plus a bonus.

Bus drivers make an average of less than $32,000 a year, and many instructional aides are making far less than that.

“When the average pay is $25,000, one out of three SEI workers are near homelessness,” said Joel Vaca, a community school coordinator. “It’s just uncalled for.”

Throughout the nation, the shortfall in school bus drivers and support staff is severe, and it’s layered onto a significant teacher shortage.

Another layer is rampant behavioral issues and learning deficits from the pandemic.

According to Pedro Noguera, the University of Southern California’s School of Education dean, it’s a lose-lose situation.

“I’m not sure what a strike will accomplish,” he said. “This is not a good thing for children, for families. At the same time, the workers have a legitimate case to make that they’re underpaid. And I think the district knows that. However, the district is in a tough bind because they don’t have the resources.”

Los Angeles Mayor Karen Bass said she is monitoring the situation and engaged with all involved parties.

During the strike, about 150 of the district’s more than 1,000 schools were expected to remain open with adult supervision but no instruction, to give students somewhere to go. Dozens of libraries and parks, plus some “grab and go” spots for students to get lunches also planned to be open to kids to lessen the strain on parents now scrambling to find care.

“Schools are so much more than centers of education — they are a safety net for hundreds of thousands of Los Angeles families,” Bass said in a statement Monday. “We will make sure to do all we can to provide resources needed by the families of our city.”

The Associated Press and NewsNation writer Devan Markham contributed to this report.