LOS ANGELES (Reuters) - California’s Democratic governor signed a law on Tuesday requiring U.S. presidential candidates to release five years of tax returns before they can appear on the state’s ballot, a move aimed squarely at Republican President Donald Trump.

FILE PHOTO: California's Governor Gavin Newsom speaks during the California Democratic Convention in San Francisco, California, U.S. June 1, 2019. REUTERS/Stephen Lam/File Photo

The law, which passed both houses of the Democrat-controlled state legislature earlier this month, marks the latest effort by Democrats to expose still-murky details of Trump’s financial empire.

“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,” California Governor Gavin Newsom said in a statement announcing the bill signing.

Newsom’s predecessor as California governor, Jerry Brown, in 2017 vetoed similar legislation passed by state lawmakers on the grounds that it might run afoul of the U.S. Constitution and set a precedent for requiring presidential candidates to disclose personal information.

“There are very good reasons why the very liberal Gov. Jerry Brown vetoed this bill two years ago - it’s unconstitutional and it opens up the possibility for states to load up more requirements on candidates in future elections. What’s next, five years of health records?,” Tim Murtaugh, communications director for the Trump campaign, said in an email.

“The Constitution is clear on the qualifications for someone to serve as president and states cannot add additional requirements on their own,” Murtaugh said. “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.”

Despite suggesting during his successful 2016 run for the presidency that he would release his tax returns once an Internal Revenue Service audit was complete, Trump has refused to make them public.

Treasury Secretary Steven Mnuchin has rejected requests by the U.S. House of Representatives’ Ways and Means Committee to the IRS to turn over six years of Trump’s returns.

The committee sued Mnuchin and the Treasury Department last week to appeal Mnuchin’s decision.

Earlier this month New York Governor Andrew Cuomo, also a Democrat, signed an amendment to a state law requiring the Department of Taxation and Finance to release any returns sought by the congressional committees.

Last week Trump sued New York over the legislation, saying it was enacted to retaliate against him because of his “policy positions, his political beliefs, and his protected speech, including the positions he took during the 2016 campaign.”