The National Labor Relations Board's acting general counsel has filed a complaint in federal court against Arizona for passing a measure that says workers can only use secret-ballot elections to determine whether they want to unionize. Organized labor prefers employees have the option of signing authorization cards to show support for unionizing.

In a complaint filed on May 6 in U.S. District Court in Phoenix, NLRB's Lafe Solomon said a 2010 Arizona constitutional amendment conflicts with federal labor law. Three other states have adopted similar measures. Solomon says he plans to file a complaint in South Dakota and may take action in South Carolina and Utah. Attorneys general from all four states said earlier this year they would “vigorously defend our laws.”