The U.S. Chamber of Commerce, the International Franchise Association, and more than a dozen other business groups secretly had “extensive input” on the NLRB’s proposal to change its legal standard for joint employer liability for labor law violations, the AFL-CIO alleges.

The labor federation said in a Dec. 7 filing to the National Labor Relations Board that the business groups submitted rulemaking petitions to the agency that appear to have substantially affected how the board wrote its proposed joint employment...