California may have swiftly passed the Presidential Tax Transparency and Accountability Act, forcing President Trump and other presidential primary candidates to disclose their tax returns if they want to be on the 2020 ballot, but the challenges have already begun.

Judicial Watch announced Monday that it filed a federal lawsuit against the state on behalf of four California voters to block the law’s implementation.

If left unchallenged, the law would force those who wish to appear on California’s March 3, 2020 presidential primary ballot to publicly disclose their tax returns for the last five years, turning them over to California’s secretary of state by November 26.

Former California Gov. Jerry Brown vetoed a similar measure last year, questioning the constitutionality of such a law and arguing that it sets a “slippery slope precedent” that could pave the way for requiring other types of documents from candidates.

“Today we require tax returns, but what would be next?" Brown asked 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."

The plaintiffs are ideologically diverse; two are Republicans, one is an independent, and one is a Democrat.

"No state or federal law has ever mandated that presidential candidates disclose their tax returns to qualify or appear on a ballot," the federal complaint says. "The voluntary release of presidential candidates’ tax returns is a recent, and partial, phenomenon, notwithstanding a current media narrative suggesting otherwise."

Judicial Watch President Tom Fitton said the “nonpartisan concern” is “about the state running roughshod and attempting to amend the Constitution on its own.”

“California politicians, in their zeal to attack President Trump, passed a law that also unconstitutionally victimizes California voters," Fitton said. "It is an obvious legal issue that a state can’t amend the U.S. Constitution by adding qualifications in order to run for president."

The Constitution only requires a presidential candidate be at least 35 years old, a natural born citizen, and have lived in the U.S. for at least 14 years.

In signing the law, Newsom released a statement arguing that California is “well within its constitutional right” to require the tax returns, issuing statements from three attorneys arguing the same.

"SB 27, which requires that presidential candidates disclose tax returns, is constitutional. It does not keep any candidate from being on the ballot so long as he or she complies with a simple requirement that is meant to provide California voters crucial information," wrote University of California, Berkeley law school dean Erwin Chemerinsky. "This is the state acting to make sure that its voters have information that might be very important to them when they cast their ballots as to who they want to be President of the United States."

Judicial Watch clearly disagrees, with Fitton noting "the courts can’t stop this abusive law fast enough.”