A report released Wednesday shows that more than 60 million workers in the United States are subject to mandatory arbitration in employment contracts, highlighting the potential scope of a key U.S. Supreme Court case that confronts the legality of those agreements.

The Economic Policy Institute's study conducted for the progressive think tank by a Cornell University professor shows the number of companies that use mandatory arbitration clauses in employment contracts has grown significantly since the 1990s.

The U.S. Supreme Court is preparing to hear oral arguments Monday in a series of consolidated cases that question the legality of clauses that limit the power of employees to join class actions against their employer. The consolidated cases before the justices are: National Labor Relations Board v. Murphy Oil USA; Epic Systems v. Lewis; and Ernst & Young v. Morris.