(Reuters) - The Department of Labor on Wednesday released a long-awaited rule requiring companies to disclose when they seek advice about countering union campaigns, which several business groups vowed to challenge in court.

The so-called persuader rule, first proposed in 2011, amends the federal Labor Management Reporting and Disclosure Act to require detailed reports from employers and their advisers, including the types of consulting or legal services rendered and any fees paid.

For more than 50 years, the reporting law required such disclosure from employers only when their lawyers or consultants interacted directly with workers.

The Department of Labor said in a memo accompanying the rule that workers would be better prepared to make decisions about unionizing if they knew who was behind their employers’ arguments. The rule is backed by major unions, including the Service Employees International Union and the AFL-CIO.

Activities covered by the rule include hiring consultants or lawyers to create materials and policies for organizing anti-union campaigns or script managers’ communications with employees.

The proposal has come under attack from groups including the U.S. Chamber of Commerce and the National Association of Manufacturers, which say it would stifle employers’ free speech rights to counter union organizing, and the American Bar Association, which says it could interfere with attorney-client privilege.

The rule is the latest salvo in the business community’s battle with the Obama administration over labor policy. Business groups compared the proposal with rules adopted last year by the National Labor Relations Board to speed up the union election process, saying both provide little benefit to workers while burdening employers.

Several business groups on Wednesday said they would probably sue over the persuader rule. They said it could discourage some companies from consulting lawyers at all, potentially leading them to commit inadvertent labor violations during union campaigns.

“The DOL must have created this rule with the real intent of assisting organized labor because they are the only ones who stand to gain anything from this,” said Robert Cresanti, president and chief executive officer of the International Franchise Association, one of the groups that says it is considering a court challenge.

Pushback was also expected from Republicans in Congress. Representative John Kline of Minnesota, who chairs the House Education and the Workforce Committee, said in a statement on Wednesday that the rule was unfair because it did not impose the same disclosure requirements on unions.