A second federal appeals court has struck down a rule that would have required millions of U.S. businesses to put up posters informing workers of their right to form a union.

The South Carolina Chamber of Commerce had challenged the rule along with the U.S. Chamber of Commerce.

A three-judge panel of the 4th U.S. Circuit Court of Appeals in Richmond ruled Friday that the National Labor Relations Board exceeded its authority when it ordered employers to display an 11-by-17-inch notice in a prominent location explaining the rights of workers to join a union and bargain collectively to improve wages and working conditions.

The posters also made clear that workers have a right not to join a union or be coerced by union officials.

More than 6 million businesses would have been subject to the rule.

Friday’s decision was another blow to the nation’s dwindling labor unions. Last month, another federal appeals court ruled that the poster rule violated businesses’ free speech rights.

In that case, the U.S. Court of Appeals for the District of Columbia Circuit sided with the National Association of Manufacturers, the U.S. Chamber and other business groups that complained the regulation violated free speech rights by forcing employers to display labor laws in a way that some believed was too skewed in favor of unionization.

“Board counsel are currently reviewing the Fourth Circuit’s decision, and the Board will make a decision on how to respond at a future time,” spokesman Henry S. Breiteneicher said in an email.

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Breiteneicher said the board also had not decided how to proceed with respect to the D.C. Circuit’s decision.

The dispute has been brewing for about two years. The original NLRB proposal triggered nearly identical federal lawsuits in the nation’s capital and in South Carolina in 2011.

The labor board has argued that the posters would help educate employees about their rights and protections under the National Labor Relations Act.

The Associated Press and The Post and Courier contributed to this report.