California Gov. Gavin Newsom (D) signed a bill into law Friday barring employers from holding mandatory anti-union meetings in the workplace.

The legislation makes California the latest and largest state to outlaw what are known as “captive audience” meetings. At least eight other states, all Democratic-leaning, have passed similar bans with the support of labor unions.

Newsom said in a statement that the legislation guarantees “the right to work without fear of retaliation.”

“California has a rich history of standing up for workers’ rights, and this bill continues that tradition ― making sure employees have the freedom to make their own decisions without coercion,” he said.

Employers hold captive-audience meetings when trying to persuade workers not to unionize, often in the weeks ahead of a union election. Many companies hire outside consultants and pay them more than $3,000 per day to lead the meetings and combat the organizing effort.

Although workers are typically told they can vote however they want, the information is almost always slanted heavily against the union.

Like legislation in other states, the California bill still allows employers to hold anti-union meetings, but they can’t force workers to show up under threat of punishment ― attendance must be voluntary. The same goes for any meeting where the employer communicates their opinions on “religious or political matters.”

When companies violate the statute, the law enables workers to pursue damages in court.

Several other states are considering similar legislation. The Economic Policy Institute, a left-leaning think tank, estimates that 60 million workers could soon be protected by such bans.

But the laws face legal challenges from employer groups, with lawsuits already filed in Connecticut and Minnesota.

The groups argue that the bans conflict with federal labor law and violate employers’ First Amendment rights. The National Federation of Independent Business alleged that the Minnesota law has already “chilled” employers’ free speech.

While states pursue their own bans, there’s also a push to outlaw captive-audience meetings at the federal level.

The National Labor Relations Board, which oversees private-sector union elections, has generally allowed employers to require workers to attend anti-union meetings over the years. However, the agency’s current general counsel, Jennifer Abruzzo, has argued in memos and cases that the mandatory nature of such meetings violates workers’ rights.

The board has not yet ruled on the issue, and a decision against employers is almost certain to wind up in federal court.

Abruzzo, appointed to her post by President Joe Biden, told HuffPost in an interview last year that captive-audience meetings are “inherently coercive.”

“There is a threat,” she said. “It’s inherent because these workers are economically dependent upon their employer. They have no true ability to exercise their right to refrain without fear of some sort of reprisal.”