Yesterday, 98 percent of teachers and staff in the Acero charter network in Chicago voted to authorize a strike. Acero, the largest network of unionized charter educators in the city, represents over five hundred members at nineteen schools across the city. Four schools associated with the Chicago International Charter Schools (CICS) network will take a strike-authorization vote this Friday.

Contrary to most media reports, this would not be the first time charter teachers have gone on strike. In 2011, roughly two dozen teachers at Philadelphia’s Khepera charter school staged a wildcat sick-out, as former teachers union organizer Shaun Richman explained in 2016. But a strike of this kind wosaruld still be historic — the first time hundreds of charter educators across two major networks have walked off the job en masse.

Perhaps we shouldn’t be surprised that this would first happen in Chicago. With an unusually high thirty-four unionized charter schools among the city’s 128 charter schools, charter unionization in Chicago has made significant headway in overturning one of corporate education reform’s hallmarks: cheap, nonunion labor.