It appears increasingly likely that employers will not have to post notices in the workplace informing employees of their right to join a union.

The United States Court of Appeals for the District of Columbia Circuit on Tuesday vacated the controversial National Labor Relations Board (NLRB) rule requiring six million private sector employers in the United States to post a notice of employee labor rights. The decision, rendered in a case brought by the National Association of Manufacturers (NAM), comes 13 months after the courts temporarily blocked implementation of the rule pending resolution of legal questions.

The three-judge appeals court panel ruled that the posting requirement compels employers to speak about employees’ labor law rights in violation of a provision of the National Labor Relations Act (NLRA) that protects employers’ rights to free speech about union issues.

The court writes that the NLRB rule violates the NLRA “because it makes an employer’s failure to post the Board’s notice an unfair labor practice, and because it treats such a failure as evidence of anti-union animus in cases involving, for example, unlawfully motivated firings or refusals to hire”in other words, because it treats such a failure as evidence of an unfair labor practice.”

AIM and other employer groups have opposed the rule as an unfair government effort to promote union organizing. The regulation is part of an ongoing effort by an activist NLRB to tilt the labor-relations playing field toward organized labor during the past three years.

“The courts have stated unequivocally that the NLRB overstepped its authority with the union-rights posting requirement,” said Michael Rudman, a labor-relations expert for AIM.

The union notice rule requires employers to post an 11-by-17-inch notice in a prominent location explaining the right of workers to join a union and bargain collectively to improve wages and working conditions. The posters also explain that workers have a right not to join a union and that it is illegal for union officials to coerce employees into unionizing.

“Stopping the NLRB’s burdensome agenda of placing itself into manufacturers’ day-to-day business operations is essential to preventing further government-inflicted damage to employee relations in the United States,” said Jay Timmons, President of NAM.

It is unclear whether the NLRB will appeal the decision to the U.S. Supreme Court.

The decision marked the latest in a series of judicial setbacks for the government agency charged with enforcing laws governing labor-management relations.

The Court of Appeals ruled in January that President Barack Obama did not have the power to make recess appointments to the National Labor Relations Board in January 2012. NLRB is appealing that decision, which could invalidate rulings, determinations and rulemaking by the NLRB over the past year.