President Donald Trump and the Republican Party are suing California over a new law requiring presidential candidates to release their tax returns to qualify for the state's primary ballot.

The two lawsuits allege that the measure is unconstitutional because it adds an extra requirement to run for president.

The law's passage came amid Trump' s yearslong refusal to release his own tax returns because he says they're under audit.

The IRS has no rule barring a person from releasing their returns if they're under audit, and Trump has given no indication that he will release his taxes ahead of next year's election.

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President Donald Trump and the Republican Party filed two lawsuits against California on Tuesday over a new law in the state that requires presidential candidates to release their tax returns to qualify for the state's primary ballot. The law does not apply to the general election.

Trump's and the GOP's lawsuits each allege California's law is unconstitutional because it adds an extra requirement to run for president and robs US citizens of their right to vote for whomever they want.

Jay Sekulow, the president's personal defense lawyer, called the law "flagrantly illegal" and added that voters decided when they elected Trump in 2016 that he didn't need to release his taxes, according to The Associated Press.

"The effort to deny California voters the opportunity to cast a ballot for President Trump in 2020 will clearly fail," Sekulow said.

Read more: California just passed a law requiring Trump to release his tax returns in order to be on the primary ballot

Tim Murtaugh, the Trump 2020 campaign's communications director, also told the Los Angeles Times last week that California's law "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."

California Gov. Gavin Newsom signed the bill into law last week after it passed the state's Democratic-controlled legislature in a party-line vote.

"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 after he signed the bill earlier this month.

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

The law's passage came amid Trump's yearslong refusal to release his own tax returns because he says they're under audit. (The IRS has no rule barring a person from releasing their returns if they're under audit.) Trump has given no indication that he will release his taxes ahead of next year's election.