Arizona and Kansas can require voters to provide proof of their citizenship when they register, if a federal judge’s ruling is upheld.

A U.S. District Judge in Kansas has ordered the federal Election Assistance Commission to help the two states enforce their laws, saying it has no legal authority to deny the addition of state-specific instructions on a national voter registration form.

The states and their top election officials, Arizona’s Ken Bennett and Kris Kobach of Kansas, sued the commission to force the change.

Both states require new voters to provide proof of citizenship to election officials. The federal registration form only requires prospective voters to sign a statement saying they’re citizens.

The states say the availability of the federal form created a loophole to their efforts to require citizenship to register. The judge said the U.S. Constitution gives the states the power to set voter registration requirements and Congress has not pre-empted that.