Stanford Law Professor David Freeman Engstrom wrote a useful op-ed in the New York Times explaining why three cases argued in the Supreme Court today are so important for workers. In brief, he notes that there are various mechanisms to protect workers including unions, government regulation, and litigation and argues that the first two of these have become less effective in recent decades. So litigation has become much more important.
Others can explain the specific legal issues and nuances of these cases, but this op-ed might be a useful start.
The cases are Epic Systems Corp. v. Lewis; Ernst & Young v. Morris; and National Labor Relations Board v. Murphy Oil USA.
