SACRAMENTO, Calif. (AP) — Four California voters have sued to block a new state law aimed at forcing Republican President Donald Trump to release his income tax returns.

Democratic Gov. Gavin Newsom signed a law last week that requires presidential candidates to file five years of their income tax returns with the California secretary of state. Candidates who don’t comply will not appear on the March 3 presidential primary ballot.

The conservative group Judicial Watch announced Monday it had filed a lawsuit last week to challenge the law. The four plaintiffs are two Republicans, one Democrat and one independent.

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

The Constitution requires three things of presidents: They have to be born in the U.S.; must be at least 35 and must have lived in the country for at least 14 years.

Attorneys for Judicial Watch argue California’s law effectively alters the Constitution by adding a new requirement for tax returns, something they say state governments don’t have the authority to do.

California’s law says voters need to know details about presidential candidates’ finances to “better estimate the risks of any given Presidential candidate engaging in corruption.”

But Judicial Watch argues that rationale could lead states to demand things like medical and mental health records and eventually things like Amazon purchases, Google search histories and Facebook friends.

The organization also argues that by limiting the law to primary elections, it does not apply to independent candidates. Judicial Watch also says the law violates voters’ constitutional rights to associate with presidential candidates and the voters who support them, rights it says are guaranteed under the First and 14th amendments.

The lawsuit names Secretary of State Alex Padilla as the defendant because his office is in charge of enforcing the law. Representatives for Padilla and Newsom declined to comment on Monday, saying they have not been officially notified of the lawsuit.

When he signed the law last week, Newsom released statements from three lawyers, including the dean of the University of California, Berkeley law school, saying the law is constitutional.

Newsom contends Congress has changed aspects of the presidency previously, including limiting presidents to two terms after President Franklin Roosevelt was elected to four terms, and passing anti-nepotism laws after President John F. Kennedy appointed his brother, Robert, U.S. attorney general.

“If the federal government is not going to act, California needs to act. We’ve always done that,” Newsom said in a video posted to his Twitter account.

Citizens have had to pay federal income taxes since 1913, but it wasn’t until 1973 when a U.S. president made his personal tax returns public. Republican Richard Nixon released his tax returns publicly while he was being audited by the IRS.

Ever since, U.S. presidents have released at least a summary of their personal income taxes. That includes most major candidates for president, with some exceptions. Former California Democratic Gov. Jerry Brown did not release his tax returns when he ran for president in 1992.

Trump has refused to release his tax returns, saying they are being audited by the IRS.