The National Labor Relations Board says it will move ahead with lawsuits against Arizona and South Dakota over state constitutional amendments that require secret ballot elections to form unions.
The move comes after weeks of negotiations that failed to reach a settlement between the federal government and attorneys general for the two states.
The agency says the amendments conflict with federal law that gives employers the option to recognize a union if a majority of workers simply sign cards that support unionizing.
Both states say they plan to vigorously defend the changes to their state constitutions approved by voters on Nov. 2.
The agency also had threatened to sue South Carolina and Utah over the same issue. Federal officials say they reserve the right to bring those cases later.