The National Labor Relations Board says that it will file lawsuits against Arizona and South Dakota for state constitutional amendments that require secret ballot elections to certify a union. The lawsuits come after months of talks between the attorneys general for both state ans the Board. The NLRB says that the amendments conflict with current federal law, and that they are pre-empted by the supremacy clause in the constitution. The states says that their laws are consistent with federal law and that the NLRB is overstepping. Talks between the state and the NLRB broke down over a confidentiality agreement, which the states said they would not agree to.
See "NLRB will sue Ariz., SD over union laws", April 25, 2011