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Teachers at the city’s Aspira charter schools have voted to authorize a strike, union leaders said Wednesday.

“We really don’t want to take it that far,” said Marines Martinez, an Aspira social studies and history teacher. “It’s just that we feel that Aspira is not negotiating with us seriously, and we want to show them how serious we are.”

No strike date has been set. Aspira operates four campuses in Chicago with an enrollment of about 1,400 students. Like other charter schools, the operation is funded by Chicago Public Schools but operates independently.

Fernando Grillo, chairman of the Aspira board, said the charter operator’s negotiators were still waiting on a counteroffer from teachers after proposing a two-year offer that would have awarded base salary increases of 2 percent per year.

The offer also would preserve Aspira’s practice of paying for the bulk of current teachers’ required pension contributions. Grillo said that so-called “pension pickup” would be scaled back for new hires.

“We’re down to the length of the agreement and what the salary is going to be,” Grillo said Wednesday.

Teachers have demanded a 3.5 percent annual pay raise, Martinez said. Teachers also say they want to force Aspira to reveal more details about its finances. Aspira officials say they’ve been forthcoming about a fiscal situation that’s crimped by a grim CPS budget.

“We’ve acted in good faith,” Grillo said. “What we need is a counteroffer so that we can get on with the negotiating process back at the table, (and) we can come to a mutually beneficial agreement that protects our mission.”

It’s the second time this school year teachers at a privately run charter network have threatened a strike. In October, a last-minute deal averted a walkout by teachers at the UNO Network of Charter Schools. The Chicago Teachers Union also came close to a strike before accepting a deal with the school board in October.

Aspira’s roughly 100 educators are represented by the Chicago Alliance of Charter Teachers and Staff, a branch of the American Federation of Teachers that oversees the city’s unionized charter school teachers.

Teachers at unionized charter networks work under separate contracts negotiated with each school operator.

Robert Bloch, a labor lawyer who also works with the CTU and other charter unions, is representing Aspira’s teachers.

Andrew Broy, head of the Illinois Network of Charter Schools, said the potential strike is the latest signal that national teacher unions hope to undermine the ability of charters to operate autonomously.

“Most of what’s driving this is the political fight over charters and the desire by ACTS to have maximum leverage in negotiations,” Broy said. “I don’t think it’s really about the management of Aspira or how well the school listens to teachers. I think it’s caught up in a larger political fight.”

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