New York City finally did the right thing last month when it decided to move forward and reopen the city’s schools on Tuesday. But that reopening won’t happen now, thanks to the city’s teachers union.

Citing concerns with the city’s safety criteria, the United Federation of Teachers threatened to strike if city officials stuck to their original reopening date. New York hasn’t had a teachers strike since 1975, and according to city law, it’s actually illegal for teachers to abandon their classrooms for the picket line. But the union’s president, Michael Mulgrew, said he would bring a strike authorization vote to the union’s delegate assembly anyway — even though there is little scientific evidence backing up the union’s health concerns.