(CNN) California Democratic Gov. Gavin Newsom signed a bill Tuesday that will require presidential candidates to disclose the last five years of their taxes in order to appear on the state primary ballot, the latest Democratic-led state to pressure President Donald Trump to reveal his financial information or risk being kept off the ballot.

The Presidential Tax Transparency and Accountability Act requires a candidate for president or California governor to file copies of their Internal Revenue Service filings for the most recent five years at least 98 days ahead of the primary election.

California's move is another step in the battle to force Trump to disclose his taxes, and the President's attorney quickly threatened to challenge the new law in court.

In 2016, Trump bucked tradition by refusing to voluntarily release his tax returns, prompting questions and lawsuits about potential conflicts of interest. Several Democratic 2020 candidates have already released their tax information, seeking to draw a contrast with Trump.

While congressional Democrats have been aiming to get a hold of Trump's taxes, California and other states -- including New York, Illinois and Washington -- pushed state legislation requiring candidates to release their individual tax returns to qualify for the presidential primary ballot.

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

Jay Sekulow, an attorney for Trump, said in a statement soon after the bill was signed, "The State of California's attempt to circumvent the Constitution will be answered in court."

California's legislature, which has a large Democratic majority in both chambers, passed the measure, Senate Bill 27 , earlier this month.

"If you are a Democrat or if you're a Republican, you can choose not to release your tax returns. You simply won't be on the California ballot," the bill's sponsor, Democratic state Sen. Mike McGuire, told CNN.

Trump has long cited an IRS audit as to why he can't release his tax returns, which McGuire dismissed as "hogwash" and argued that Trump "simply wants to avoid releasing his tax returns."

"California didn't pick this fight. President Donald Trump has gone against 40 years of tradition in this ... in our country that has made our country stronger," McGuire told CNN.

McGuire said that the measure "applies to all candidates. It doesn't discriminate. And that's why I believe that this bill will be ruled constitutional."

Republicans, however, expect the law to be challenged in court.

"I think that it's going to be locked up in courts. I think it's very clear to many people, even Democrats, that this is completely unconstitutional," California GOP chair Jessica Patterson told CNN, adding that the motivation behind the bill is "clearly a vendetta with President Trump."

Republican state Sen. Brian Jones predicted that if Trump's name isn't on the California ballot, the GOP could use it as a tool to energize his base.

"People are like OK, I don't like Trump, but I don't like this idea either of the state, the majority party overreaching. So I'm going to go vote just to show my distaste of this process," Jones told CNN.

Former California Gov. Jerry Brown, a Democrat, had vetoed a similar measure back in 2017 , questioning the constitutionality and concerned that it sets a "slippery slope" of what individual states could require of candidates in the future.

"Today we require tax returns, but what would be next?" Brown said at the time. "Five years of health records? A certified birth certificate? High school report cards? And will these requirements vary depending on which political party is in power?"