Tens of thousands of workers in the Los Angeles Unified School District planned to walk off the job Tuesday over stalled contract talks, and they will be joined in solidarity by teachers in a three-day strike that will shut down the nation's second-largest school system. Demonstrations are expected at schools across the city 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. The workers were expected to join picket lines before dawn, demanding better wages and increased staffing. The district has more than 500,000 students from Los Angeles and all or part of 25 other cities and unincorporated county areas. 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. Local 99 said Monday evening that it was in discussions with state labor regulators over allegations that the district engaged in misconduct that has impeded the rights of workers to engage in legally protected union-related activities. “We want to be clear that we are not in negotiations with LAUSD,” the union said in a statement. “We continue to be engaged in the impasse process with the state.” Those talks would not avoid a walkout, the statement said. “We are ready to strike,” the union said. The Local 99 president, Conrado Guerrero, told TV station KABC that the union has made it clear how a strike can be avoided. "The only thing that will stop it is a 30% plus two dollar equity pay wage increase to bring us back to the table." During the strike, about 150 of the district's more than 1,000 schools are 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. Mike Bernstein, a parent, told KABC-TV that he's worried how the strike will impact children. "I support my kids and ultimately I think they're being left behind." Jenna Schwartz, also a parent, explained her support for the union. "We have some of our most underpaid workers doing some of the most challenging jobs on our campuses. The majority aren't receiving health care, they've been negotiating for years," she said.