The National Association of Manufacturers is making oral arguments today in a lawsuit against the National Labor Relations Board, but the lobbying group hasn’t limited its fight to the courtroom.

NAM, which is suing the board for issuing a rule that would require employers to post a notice of employee rights at workplaces, has taken its message to Capitol Hill and to the public. NAM argues that the board does not have the authority to make the rule.

“We believe that it is solely within the purview of Congress to determine the expansion of or redefinition of an unlawful labor practice or an unfair labor practice,” NAM Vice President for Human Resources Policy Joe Trauger said in a Friday conference call with reporters.

NAM isn’t the only business group to take on the board. The National Federation of Independent Business’ suit was consolidated with NAM’s. And Rep. John Kline (R-Minn.), chairman of the Education and Workforce Committee, and 35 other Members filed an amicus brief in support of NAM’s case.

Trauger added that the poster rule is just one example of the NLRB’s “activist agenda,” which could have dire consequences on employers and jobs. NAM’s internal polls show that nearly 70 percent of its members indicated that the board’s actions including the notice posting “would have a negative impact on their ability or willingness to expand and hire,” Trauger said.

NAM’s legal complaint also says the posting notices would violate employers’ freedom of speech.

A spokeswoman for the NLRB said the agency typically doesn’t address pending litigation, but she referred comments to a posting of the rule in the Federal Register. The 1935 National Labor Relations Act gives employees the right to organize or join labor unions and to engage in collective bargaining, but “For employees to fully exercise their NLRA rights, however, they must know that those rights exist and that the Board protects those rights,” the Federal Register notice said.

It added that the NLRB has reason to believe most employees do not understand those rights. And so even though the board “agrees that it may not exercise its rulemaking authority in a way contrary to that intended by Congress,” it does not believe it is doing so with this rule.

Nancy Schiffer, associate general counsel of the AFL-CIO, which is not involved in the court case, said she had trouble understanding the controversy over the rule requiring the workplace posters given that other similar employee notices, such as those for workers’ compensation, are already posted on the job.

“It seems so reasonable and rational that employees would get to know what their rights are,” she said.

She also called the NAM charges of an activist NLRB “unfair.” She said that in 2007 during the George W. Bush administration the NLRB made numerous decisions that cut back on workers’ rights.

“To charge that an agency that’s actually doing what it’s supposed to be doing is activist is just another way of saying this agency ought to fold up its tent and go away,” she said.

The poster rule is not the only issue the business community has with the NLRB, which filed suit against Boeing Co. for retaliating against union strikes. That suit was settled recently, but it hasn’t healed the split between the two sides.

In addition, President Barack Obama withdrew the nomination of Craig Becker, a former union lawyer who was a recess appointee to the board. And the president announced his intent Dec. 14 to nominate Sharon Block, a former Senate Health, Education, Labor and Pensions Committee aide to then-Sen. Edward Kennedy (D-Mass.), and Richard Griffin, who is general counsel for the International Union of Operating Engineers, as members of the board.

Trauger said his group didn’t want to rush to judgment on the nominees, but he indicated a concern that the president would make recess appointments again. And Trauger said he was worried about the nomination of another union counsel.

“That is very, very troubling,” he said.