Teachers at 15 Chicago charter schools voted on Tuesday to authorize a strike, taking another step toward becoming the first group of charter school educators in the country to hit the picket line.

Ninety-eight percent of the more than 500 Acero school educators voted to approve a potential work stoppage, though Chicago Teachers Union leaders held off on announcing a strike date ahead of a bargaining session scheduled for Friday.

“We deserve the same pay and benefits for doing the equal work that’s done across the rest of the school system in the city of Chicago,” CTU president Jesse Sharkey said Tuesday night at the union’s West Town headquarters.

Acero administrators said they were “disappointed” in the vote.

“It is unfair to parents and students to threaten to disrupt classes when Acero Schools is more than willing to continue negotiations and work with the federal mediator brought in this weekend,” Acero’s chief external affairs officer Helena Stangle said.

“Regardless, we will continue to negotiate in good faith. We are committed to reaching an agreement that provides a reasonable and competitive compensation package for our teachers and staff while maintaining the best possible educational outcomes for our students.”

Acero teachers are seeking pay raises, smaller class sizes, improved special education resources and extended parental leave. The union also wants Acero to increase diversity among mostly white teachers in the largely Hispanic charter network by creating a path for paraprofessionals to become teachers.

Their contract expired in August, and Acero has said the union most recently rejected their proposal that would have raised the average teacher salary by about 5 percent to $67,937.

The union says charter networks rake in 8 percent more funding per pupil compared to Chicago Public Schools rates, while charter teachers’ salaries are 30 percent lower — a claim Acero CEO Richard Rodriguez called “antithetical to what we’ve all known to be true.”

Addressing the Acero school board last week, Rodriguez acknowledged their teachers make less than the average CPS salary, but said the charter “operates more like a household, that must budget.”

“The Chicago Public Schools operate with billions of dollars and have the full faith and credit of the city of Chicago to back them up. Unlike CPS, we don’t have a rich uncle,” Rodriguez said.

The Acero teachers announced the strike vote last week. Teachers at four Chicago International Charter School locations — ChicagoQuest North, Northtown, Wrightwood and Ralph Ellison — will vote Friday on whether to join the strike threat.

If that vote passes as expected, a full strike potentially would include about 700 teachers from the 19 schools, affecting more than 8,000 students.

Teachers at the Acero schools previously voted to authorize a strike in 2016, when Acero was known as UNO and before the charter teachers union merged with the CTU. A last-minute deal was struck before a work stoppage.

Strikes also have been narrowly averted at ASPIRA and Passages charter schools over the last two years.

Teachers have never gone on strike at any charter school in the United States.