WASHINGTON (AP) - A prominent business group filed a lawsuit Wednesday challenging government rules that require federal contractors to display posters telling workers they have a legal right to form a union. The National Association of Manufacturers asserts the Labor Department regulations violate the free speech rights of employers by forcing them to promote unionization of their work forces or risk losing their federal contracts. Federal officials say the posters simply inform workers of their legal rights. Earlier this year, a federal appeals court struck down a similar rule from the National Labor Relations Board that would have affected a much wider swath of business. The Labor Department rules, which have been in place since 2010, affect federal contractors and subcontractors that employ roughly 22 percent of the workforce - about 16 million workers. "The courts have already ruled that these posters amount to compelled speech and extend beyond the intent of the National Labor Relations Act," said Linda Kelly, NAM Senior Vice President and General Counsel. Federal contractors deserve the same protection from this aggressive overreach. A Labor Department spokesman did not immediately respond to a request for comment. The rules, approved by the Labor Department's Office of Labor Management Standards, implemented a White House executive order signed by President Barack Obama shortly after he took office in 2009. With union membership on the decline, union leaders hoped the posters would give them a small boost in organizing efforts. Obama's executive order rescinded a prior executive order from President George W. Bush that required federal contractors to post a notice informing employees of their rights not to join a labor union or pay fees for union expenses that are unrelated to representation issues. Bush's order was known as the "Beck Rule" after the Supreme Court's decision in Communications Workers of America v. Beck, which set forth the rights of employees. The 11 by 17 inch posters advise employees of their legal rights to organize unions, bargain collectively, and go on strike and picket without retribution by an employer. The posters also inform workers of their rights not to join a union or be coerced by union officials. NAM officials say they are not aware of any of their members being debarred or losing federal contracts over failure to display the posters. The rules are enforced by Labor's Office of Federal Contract Compliance Programs, which polices employment discrimination by federal contractors. Although the Labor Department rule has been in place for more than three years, Kelly said her group is challenging it now because of the precedent set earlier this year by the U.S. Court of Appeals for the District of Columbia Circuit. In striking down a similar poster rule from the NLRB, the court found employers have the right not to display the government's poster on union rights if they found the language in it objectionable. Employers already have to display other posters explaining federal antidiscrimination law and workplace safety rules, but those are mandated by Congress.