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A teachers strike in the nation’s second-largest school district was set to begin Monday in Los Angeles after union and district officials sat out last-minute bargaining sessions.

The decision, described by union officials Sunday as a “last resort,” came after nearly two years of failed efforts to negotiate a new contract for educators in the Los Angeles Unified School District, as well as a flurry of offers made by the district last week that the union described as inadequate.

“We have not received a proposal over the weekend,” United Teachers of Los Angeles secretary Arlene Inouye said in a Sunday news conference. “We will be striking tomorrow.”

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United Teachers Los Angeles leaders, joined by thousands of teachers, march past the Walt Disney Concert Hall in Los Angeles last month. Damian Dovarganes / AP file

Union officials declared an “impasse” in negotiations on Friday, saying an offer from the district to raise salaries, cap class sizes and hire 1,200 additional staff was good for only one year. Nor had the district followed up on a promise, they said, to examine what union president Alex Caputo-Pearl called an “existential threat” — the impact of non-union charter schools on the city’s public schools.

Shannon Haber, a school district spokeswoman, could not say Sunday whether the district offered to resume talks over the weekend. But she did say that district superintendent Austin Beutner has said he would meet with union negotiators “anytime, anywhere.”

In a statement Sunday, the district said instruction would continue at elementary, middle and high schools throughout the strike, though preschools would be closed and early education centers would be open only for special needs students.

“Los Angeles Unified did not want a strike,” the statement said, citing its offer of 1,200 additional staff members. “Los Angeles Unified remains committed to contract negotiations and will continue to work around the clock to find solutions to end the strike which will hurt students, families and communities most in need throughout Los Angeles."

Teachers have described Monday’s strike as a last stand against decades of defunding public schools, a point emphasized by union officials Sunday.

“We’re in a battle for the soul of public education,” said Pearl-Caputo, whose union represents more than 30,000 teachers.

The strike, which will mark the first teachers walkout in Los Angeles in three decades, is scheduled to begin Monday at 7:30 a.m. with a march from Los Angeles City Hall to the school district’s headquarters, one mile away.