TRENTON -- Gov. Chris Christie on Monday vetoed a controversial bill that would have forced future presidential candidates -- including President Donald Trump -- to release their tax returns to receive a spot on New Jersey's ballot.

The governor, a longtime Trump friend and fellow Republican, dismissed the Democratic-backed measure as "clearly unconstitutional" and a "transparent political stunt masquerading as a bill."

"Unwilling to cope with the results of last November's election, the Legislature introduced this unconstitutional bill as a form of therapy to deal with their disbelief at the 2016 election results, and to play politics to their base," Christie wrote in his veto message.

Christie actually used a conditional veto, in which governors suggest changes to bills that the state Legislature can then choose to make.

But Christie's condition would rewrite the bill rather than change it. He eliminated the part requiring presidential contenders to disclose tax returns and recommended expanding the state's Open Public Record Act by removing exemptions for records kept by the state Legislature.

"The hypocrisy and false outrage underlying this bill is stunning -- even by Trenton standards," Christie wrote. "Rather than focus on the multitude of important issues impacting New Jersey's residents, the Legislature wasted time on a bill that manufactures from whole cloth a qualification for the office of President not found in the United States Constitution in the hope of scoring cheap political points.

"Although I have strong doubts that the Legislature has any real interest in promoting greater transparency, I am recommending changes to the bill that would fit the old saying, 'Doctor, heal thyself,'" he added. "If transparency is what the legislature wants, let's get our own house in order first.

At least 21 states introduced similar bills after Trump won the 2016 presidential election. But New Jersey's legislature -- win which both houses are controlled by Democrats -- was the first to pass such a bill.

Though it's not required by law that presidential contenders make their tax returns public, Trump became the first major-party candidate in 40 years not to do so, saying he wouldn't until the Internal Revenue Service was finished with an audit. He still refuses to release them now that he's in office.

Last week, U.S. Treasury Secretary Steve Mnuchin said Trump doesn't plan to make the documents public and that Americans already have "plenty of information" about the president's finances.

State Assemblyman John McKeon (D-Essex), one of the sponsors of the Democratic measure, said Christie's veto was "sadly not surprising, nor is his grandstanding and childish rhetoric." He also mocked the governor for using the kind of language Trump often uses on Twitter.

"Gov. Christie is obsessed with protecting and showing allegiance to President Trump," McKeon added. "This bill wasn't about President Trump. 2016 is over. Donald Trump is the president. This bill was about going forward, yet all Gov. Christie can think about is his ally Donald Trump. Sad!"

The bill would (S3048/A4520) have required both presidential and vice presidential candidates to release five years of their personal income tax returns. That would include Trump, a former Atlantic City casino tycoon, should he run for re-election in 2020.

The state Senate passed the measure, 24-11, and the state Assembly approved it, 48-26. Both votes were mostly along party lines.

Critics say Trump's tax returns would show if he has any conflicts of interests related to his business ties.

"The people of the United States deserve to known where presidential candidates earn their money," McKeon said.

Opponents argued that the U.S. Constitution bars states from adding requirements for who can run for president.

Democratic leaders have suggested they might try to override Christie's veto on the measure or simply introduce the measure again after Christie leaves office in January and a new governor takes over. A Democrat is favored to win this year's race to succeed Christie.

The Associated Press contributed to this report.

Brent Johnson may be reached at bjohnson@njadvancemedia.com. Follow him on Twitter @johnsb01. Find NJ.com Politics on Facebook.