The National Labor Relations Board ruled that employers can’t force workers to listen to anti-union speeches, but a Trump board could reverse the decision.

Employers can still hold meetings to express their views on unionization, but must now give workers advance notice and make clear they are voluntary.

The board's ruling responds to a series of labor complaints against Amazon for engaging in union-busting tactics.

Amazon also removed union-related posts on an internet message board and threatened to discipline a JFK8 employee if she re-posted them, the board found. Workers at the warehouse ultimately voted to join the Amazon Labor Union, making it the first and so far only Amazon facility to unionize.

Mandatory “captive audience” meetings in which companies argue against unionization are illegal, the National Labor Relations Board ruled in a case involving Amazon.com Inc., prohibiting one of employers’ most potent weapons against labor organizing campaigns.