LOS ANGELES (AP) — Teachers in the Los Angeles Unified School District voted Friday to authorize a strike if labor negotiations continue to stall.

United Teachers Los Angeles announced that an overwhelming 98 percent of voting members favored giving the union the authority to call a strike; a walkout hasn't happened since 1989.

The vote comes amid a stalemate in contract talks with the nation's second-largest school district, which has more than 640,000 students.

UTLA said the vote doesn't necessarily mean a strike will happen. But teachers are ready to hit the picket lines if the union and district fail to reach an agreement that addresses teachers' demands on pay raises, smaller class sizes and other issues.

The district said a strike will hurt students and families and it hopes to reach an agreement.

"The force behind this overwhelming vote is clear," Arlene Inouye, chair of the UTLA bargaining team, said at a news conference.

The union said it was prepared to begin mediation with the school district by mid-August, but the district refuses to negotiate a fair agreement and delayed mediation sessions until Sept. 27.

However, the district said while it accepted the Sept. 27 offered by the state mediator, it is willing to explore any avenue that helps resolve the issues.

Both the district and the union have filed charges against the other.

The union filed an unfair labor practice charge against the district on Monday for unlawful interference with the union's strike-authorization vote and for failure to provide requested financial documents.

The district followed suit Tuesday, accusing the union of engaging in "take-it-or-leave-it bargaining" and "making no compromises toward reaching an agreement."

"UTLA openly talked about a strike long before the parties even began negotiations, let alone reached impasse," General Counsel Dave Holmquist said in a statement.

Teachers around the nation have been pursuing better contracts with walkouts and protests. The movement started earlier this year in West Virginia, where a strike resulted in a raise, and spread to Oklahoma, Kentucky, Colorado, Arizona and Washington state.