Today, the National Labor Relations Board (NLRB) took steps to enforce workers’ rights as guaranteed by U.S. law. The board advised the attorneys general of Arizona, South Carolina, South Dakota and Utah that so-called secret ballot amendments to their state constitutions are pre-empted by the National Labor Relations Act, which offers workers two paths to choosing a union.

The board also has authorized its acting general counsel to file federal lawsuits, if necessary, to stop the states from enforcing the laws. The amendments have already taken effect in South Dakota and Utah and are expected to become effective soon in Arizona and South Carolina.

Under the  federal law, workers may choose a union by voting in a secret-ballot election conducted by the NLRB or they may persuade an employer to voluntarily recognize the union after a majority sign authorization cards. Because the state amendments in question prohibit the voluntary recognition option,  they “interfere with the exercise of a well-established federally protected right,” the NLRB said in a release.

You can read the NLRB release here.