Millions of businesses won’t be required to display posters explaining union rights to workers because the issue is being appealed.

The National Labor Relations Board rule was supposed to take effect April 30.

But the U.S. Court of Appeals in Washington, D.C., agreed Tuesday to temporarily block the measure so it can hear a challenge from the National Association of Manufacturers.

The pro-business trade group is seeking to overturn a lower court’s decision in March that found the NLRB has the power to require the posters.

Senior U.S. District Court Judge David Norton of Charleston added a new wrinkle to the debate Friday when he found that the labor board had overstepped its boundaries. The NLRB said Tuesday it plans to appeal his decision.

Jay Timmons, chief executive officer of the National Association of Manufacturers, cited Norton’s ruling in a written statement.

“The decision last week by the South Carolina District Court correctly reined in the NLRB’s egregious overreach in its authority, and today’s injunction is a positive step in overturning this harmful rule,” Timmons said Tuesday.

NLRB said through Chairman Mark Pearce that it would stand its ground, though it has instructed its regional offices not to implement the rule until the appeals are resolved.

“We continue to believe that requiring employers to post this notice is well within the board’s authority, and that it provides a genuine service to employees who may not otherwise know their rights under our law,” Pearce said Tuesday.

Business groups have argued the posters are an unfair government mandate that promote union organizing and infringe on their free-speech rights.

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

The rollout of the rule had been postponed twice before Tuesday.

The NLRB proposal triggered nearly identical federal lawsuits in the nation’s capital and in South Carolina last year.

In the Washington case, which was filed by the manufacturers association, Judge Amy Berman Jackson found that the NLRB has the power to require the union displays.

“The notice-posting rule is a reasonable means of promoting awareness,” she wrote last month.

The U.S. Chamber of Commerce filed a separate challenge in Charleston in September.

In that case, Norton ruled last week the posting requirement exceeds the NLRB’s power. He wrote that “there is not a single trace of statutory text that indicates Congress intended for the board to proactively regulate employers in this manner.”

The NLRB is pushing to have the 11-by-17-inch posters displayed prominently at about 6 million businesses. The notices would explain the rights that employees have under federal law, such as forming or joining a union, distributing union literature, collective bargaining and picketing. The posters also show examples of illegal union conduct.

Reach John P. McDermott at 937-5572.