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.

Unions said captive audience meetings were partially responsible for losses at the Amazon location in Bessemer and the Mercedes plant.

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 ruling, stemming from a complaint against Amazon, bars companies from compelling workers to attend meetings on unionization’s downsides.

The decision passed 3-1, with the NLRB General Counsel, Jennifer Abruzzo, arguing the meetings violated worker’s rights, as they were forced to attend and be subjected to the company’s anti-union messaging.

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.

Large employers including Amazon, Starbucks, Trader Joe’s and REI have responded to increasing attempts to unionize by holding captive audience meetings.

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.