Teachers in the Oakland Unified School District voted Monday to allow union leaders to call a strike.

The decision comes after a year and a half of failed contract negotiations between the district and union.

Teachers overwhelmingly passed the decision to strike, with 95 percent of the participating educators voting "Yes." Union officials said there was a huge turnout and that 84 percent of union members voted.

Oakland teachers have been working without a contract for 18 months and are demanding a 12 percent raise over three years, as well as smaller class sizes. The district said it wants to pay teachers more, but add it cannot afford a higher pay bump while trying to avoid a budget deficit.

The district's latest offer was a 5 percent raise over three years. OUSD officials say they have too many schools and not enough kids. In order to give teachers a pay hike, the district said it will have to cut tens of millions of dollars from other parts of the school system, including the central office.

"Everybody here knows that they deserve a raise, and want to give them a raise," OUSD spokesman John Sasaki said. "It's just a matter of how much can we give."

Keith Brown with the Oakland Education Association said teachers expect to be on strike by the end of the month.

"If the school board won't act, we will act!" Brown said.

The district will have to scramble to replace or do without 3,000 teachers, counselors, nurses, psychologists, librarians, speech pathologists and social workers if the union goes on strike later this month.

A spokesperson for the district said they are preparing for a strike, but there are not enough substitute teachers available for every classroom.

If a strike were to happen, it would have to be after Feb. 15 because that is when a state-appointed fact-finder is set to release a report on the facts surrounding this contract dispute.

The strike cannot legally happen until the report is released.