California Gov. Gavin Newsom Gavin NewsomOVERNIGHT ENERGY: California seeks to sell only electric cars by 2035 | EPA threatens to close New York City office after Trump threats to 'anarchist' cities | House energy package sparks criticism from left and right California seeks to sell only electric cars by 2035 EPA head questions connection of climate change to natural disasters MORE (D) on Tuesday signed a bill requiring President Trump Donald John TrumpSteele Dossier sub-source was subject of FBI counterintelligence probe Pelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Trump 'no longer angry' at Romney because of Supreme Court stance MORE to release his tax returns before he can appear on the state's 2020 primary ballot.

Under S.B. 27, called the "Presidential Tax Transparency and Accountability Act," any candidate running for president or governor of California will be required to file copies of the last five years of their tax returns to the California secretary of State.

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"As one of the largest economies in the world and home to one in nine Americans eligible to vote, California has a special responsibility to require this information of presidential and gubernatorial candidates," Newsom said in a statement.

"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. The disclosure required by this bill will shed light on conflicts of interest, self-dealing, or influence from domestic and foreign business interest."

In a statement, Trump campaign spokesman Tim Murtaugh called the move "unconstitutional."

"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?" he said.

Murtaugh said states cannot add requirements to presidential candidates' qualifications for running.

"The Constitution is clear on the qualifications for someone to serve as president and states cannot add additional requirements on their own," he 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."

The bill was overwhelmingly approved by the State Assembly and Senate earlier this month.

It includes an “urgency clause,” meaning it would take effect immediately and force the candidates running for president in 2020 to disclose their financial statements.

In a statement, progressive group Americans for Tax Fairness praised the bill as a win for transparency and accountability.

“This bill was necessary because President Donald Trump has departed from over four decades of established political tradition, respected by both Democrats and Republicans alike, by refusing to release his income tax returns,” Executive Director Frank Clemente said in a statement. “He has denied voters the opportunity to fully evaluate his fitness for the office.”

While Trump is unlikely to pick up California's electoral college votes regardless of whether he is on the ballot, the push underscores efforts by Democrats to obtain information about his finances.

The legislation comes amid a growing battle between Trump and House Democrats over his tax returns, which he has long refused to release.

The Ways and Means Committee earlier this month filed a lawsuit over the administration’s refusal to release the returns, kicking off what is likely to be a lengthy legal battle.

Trump last week also filed a lawsuit over a new New York law that allows Congress to request his state tax returns.

The president isn't likely to have a problem securing the GOP presidential nomination regardless of California's move.

Former Massachusetts Gov. William Weld William (Bill) WeldRalph Gants, chief justice of Massachusetts supreme court, dies at 65 The Hill's Campaign Report: Biden visits Kenosha | Trump's double-voting suggestion draws fire | Facebook clamps down on election ads Biden picks up endorsements from nearly 100 Republicans MORE is the only Republican candidate to formally announce a primary challenge to Trump so far in the 2020 presidential race.

The Republican National Committee (RNC) has already voted to express its “undivided support” for Trump as its 2020 nominee, and Trump's reelection campaign has staffed up with party insiders to line up its delegate strategy well ahead of the party's nominating convention.

--Updated 2:54 p.m.