California Gov. Gavin Newsom (D) signed a tax transparency bill on Tuesday that will require presidential and gubernatorial candidates to disclose their tax returns in order to appear on the state’s primary ballot.

With Congress tied up in the courts to get ahold of President Donald Trump’s tax returns, several states have taken the issue into their own hands.

“These are extraordinary times and states have a legal and moral duty to do everything in their power to ensure leaders seeking the highest offices meet minimal standards, and to restore public confidence,” Newsom said in an official statement after signing the bill. “The disclosure required by this bill will shed light on conflicts of interest, self-dealing, or influence from domestic and foreign business interest.”

The Trump campaign slammed the California law as “unconstitutional.”

“The Constitution is clear on the qualifications for someone to serve as president and states cannot add additional requirements on their own,” campaign communications director Tim Murtaugh told the Hill. “The bill also violates the 1st Amendment right of association since California can’t tell political parties which candidates their members can or cannot vote for in a primary election.”

New York Gov. Andrew Cuomo (D) signed a bill earlier this month that would allow the state’s Department of Taxation and Finance commissioner to hand over state tax returns to Congress’ Ways and Means Committee, the Senate Finance Committee, and the Joint Committee on Taxation.