Around 3,000 graduate workers at Columbia University have been on strike since November 3rd. On December 2nd, Columbia’s human resources office sent an email informing workers that their positions would be replaced if their strike continues past December 10th. The worker’s union has already filed two unfair labor practice charges with the NLRB, and they now think that sending this email was unlawful as well. Columbia says this move is necessary to fulfill their commitment to their students and completely lawful.
See "Columbia threatens to replace their striking graduate workers", Michael Sainato, The Guardian, December 9, 2021