Employers can’t fire or otherwise punish workers for filing class or collective actions to improve workplace conditions, the National Labor Relations Board ruled Aug. 14.

The decision clears up uncertainty about the board’s views on protections for group lawsuits following the U.S. Supreme Court’s ruling last year in Epic Systems v. Lewis. The high court’s decision, which permitted class-action waivers in arbitration agreements, said it seemed “pretty unlikely” that federal labor law protects filing class or collective actions.

But the NLRB’s new ruling, in a case involving Cordua Restaurants Inc., also gives employers more leeway with how they handle their...