The Chicago Tribune reports that Chicago Public Schools is bringing charges against the Chicago Teachers Union over a one-day strike that took place April 1.

District CEO Forrest Claypool says the district wants a permanent injunction against similar one-day strikes. The district is also seeking damages resulting from the strike. “[We have to] know with certainty that CTU leadership can’t, at their own whim, say ‘We’re going to shut down the schools’ without following the law,” Claypool said at a news conference.