Southwest Airlines has decided to sue the union that represents its mechanics. The company is alleging that the union has caused slowdowns that have resulted in flight cancellations. Additionally, the company has alleged that mechanics have been unnecessarily deeming planes unsafe, in order to ground them and disrupt flights. As of now, the union has not responded to comment requests.
See "Southwest Airlines Sues Mechanics in Labor Dispute", Zach Wichter, The New York Times, March 1, 2019