WASHINGTON -- Though every major party nominee since 1976 has released his tax returns while running for president, the practice has never been required by law. Sen. Ron Wyden (D-Ore.) wants to change that.

The senior Democrat on the Senate Finance Committee, which handles tax issues, introduced a bill on Wednesday that would force presidential candidates to release their most recent tax returns. The Presidential Tax Transparency Act, as the bill is called, would require candidates to make their latest three years of tax returns public no later than 15 days after becoming the nominee. If they do not comply, the treasury secretary would be directed to do so for them, provided the appropriate redaction of sensitive personal information.

"Since the days of Watergate, the American people have had an expectation that nominees to be the leader of the free world not hide their finances and personal tax returns,” Wyden said in a statement.

“Tax returns deliver honest answers to key questions from the American public,” he added. “Do you even pay taxes? Do you give to charity? Are you abusing tax loopholes at the expense of middle class families? Are you keeping your money offshore? People have a right to know.”

Only one major party presidential candidate is refusing to release any of his tax returns to the public right now, and his name is Donald Trump. The presumptive GOP nominee has said he cannot release his returns because they are currently under audit by the Internal Revenue Service. The IRS, however, has clarified there is nothing legally preventing someone from making a return public while it's under audit.

Trump's campaign has argued that Americans simply aren't interested in the Manhattan real estate mogul's tax returns. Corey Lewandowski, Trump's campaign manager, on Tuesday even claimed that there is "nothing to learn” from them.

"I strongly disagree with that," Wyden told The Huffington Post on a Wednesday call with reporters. "For literally four decades now, Democrats, Republican, candidates regardless of party have made this information available."

Indeed, there is evidence that refusing to release any returns may hurt Trump in the general election. According to a Morning Consult survey released Tuesday, 67 percent of registered voters — including 60 percent of Republicans — said presidential candidates should release their tax returns.

Senate Democrats have stirred the pot on the issue of tax returns before. During the 2012 election, then-Senate Majority Leader Harry Reid (D-Nev.) infamously claimed that Mitt Romney paid no taxes, upping the pressure on the Republican standard-bearer to release his tax returns. When he finally did so, they showed he paid a low 14 percent tax rate in 2011.

Asked on the call whether he had any communication with the campaign of Democratic presidential hopeful Hillary Clinton, Wyden said only that he had not spoken to the former secretary of state.

It is questionable how far such a bill would go in a Republican-controlled Senate that is slowly coming around to supporting their nominee. But Wyden said he would try to round up GOP co-sponsors anyway, feeling encouraged by recent comments by Senate Majority Leader Mitch McConnell (R-Ky.), who said that "most candidates" have released returns under a long-standing "tradition."

Wyden also batted down a question about whether his bill, which would force nominees to release private information, conflicted with his strong stance in support of privacy. The senator from Oregon has been a vocal critic of government surveillance programs, such as those revealed by National Security Agency leaker Edward Snowden.

He noted that nominees seeking confirmation before the Senate Finance Committee, for example, must also submit such personal information.

"If somehow we're breaking a tradition here as presidential nominees by making this information available, we're saying the commander in chief is held to a standard lower than an assistant secretary," he said.

Editor’s note: Donald Trump regularly incites political violence and is a serial liar, rampant xenophobe, racist, misogynist and birther who has repeatedly pledged to ban all Muslims — 1.6 billion members of an entire religion — from entering the U.S.