Chicago Teachers Union members have signaled that they are ready to walk off the job for the second time in three years, with 88 percent voting to authorize a strike, union leaders announced Monday.

The vote is just the first step in a months-long process that would have to play out before teachers actually decide to walk off the job. But it is an important negotiating tool for teachers because it ratchets up the pressure on Mayor Rahm Emanuel, who already has enough political problems: Last week, protesters took to the streets to call for his resignation after he apologized for how he handled a police officer’s fatal shooting of 17-year-old Laquan McDonald.

The teachers’ contract expired in June, and efforts to reach a one-year contract agreement with Chicago Public Schools fell apart during the summer amid differences over teacher evaluations, among other issues. Talks between the union and the nation’s third-largest school system restarted in August, but the two sides have been unable to reach a compromise on a number of issues, including staffing, salaries, pension contributions and health-care benefits.

Under state law, 75 percent of the union’s active members must vote yes in order to authorize a strike. The union easily met that bar: Ninety-two percent of the union’s 27,000 members voted during a three-day window last week, and of those who cast ballots, 96.5 percent voted in favor of backing a strike, according to the Chicago Sun-Times.

Negotiations are taking place against the backdrop of a $500 million budget gap that has already led to hundreds of layoffs in recent months and could lead to thousands more. Union leaders argue that the cuts are leaving inner-city schools without necessities — such as librarians and special education teachers — that suburban schools can take for granted.

“We’re not going to take it lying down, these cuts. We’re not going to treat it like a fait accompli that cuts are coming,” Jesse Sharkey, vice president of the Chicago Teachers Union, said Monday, according to the Sun-Times.

According to the union, the Chicago school board — whose members are appointed by the mayor — has proposed changes that would amount to a 12 percent cut in total compensation over a three-year term.

The school board also has rejected union proposals for smaller class sizes and more librarians, counselors, social workers and art and music programs, according to the union, as well as proposals that would cost little to nothing, such as doing away with redundant testing and giving teachers more autonomy in grading student work.

Chicago Public Schools officials said it is premature for the union to threaten a strike because the mediation process is not complete. School system officials said the union’s proposal would cost an additional $1.5 billion in spending, which they call unrealistic for a district in a serious financial crunch.

Schools officials said that state lawmakers hold the key to the bridging the shortfall, noting that Chicago students comprise 20 percent of the state’s students but receive only 5 percent of state education funding.

“We have the highest respect for our teachers’ work and while we understand their frustrations, a strike that threatens to set back our students’ progress is simply not the answer to our challenges,” Chicago Public Schools CEO Forrest Claypool said in a statement.

“So rather than strike, we ask that the Chicago Teachers Union join us to fight for our shared goal of equal education funding from Springfield for Chicago’s children. We will continue to negotiate in good faith with the CTU leadership to reach a fair, multi-year agreement that protects teachers, their jobs and ensures our students’ success.”

The mayor’s press office did not immediately respond to a request for comment on Monday.