After Romney said Thursday Reid should "put up or shut up" on a charge Romney paid no taxes for a decade, Reid, D-Nev., issued a statement insisting his source for the allegation is "extremely credible," and repeating his challenge that Romney should prove he paid his taxes.
"When it comes to answering the legitimate questions the American people have about whether he avoided paying his fair share in taxes or why he opened a Swiss bank account, Romney has shut up," Reid said. "But as a presidential candidate, it's his obligation to put up, and release several years' worth of tax returns just like nominees of both parties have done for decades."
The statement reiterated a claim Reid made on the Senate floor Thursday.
"Let him prove that he has paid taxes, because he hasn't," Reid said.
"Mitt Romney makes more money in a single day than the average middle-class family makes in two years or more," he added.
Reid has provided no proof for his repeated assertion about Romney's taxes.
"It's time for Harry to put up or shut up," Romney said in a radio interview Thursday with right-wing talk show host Sean Hannity.
"Harry's gonna have to describe who it is he spoke with because of course that's totally and completely wrong," Romney told Hannity. "It's untrue, dishonest and inaccurate. It's wrong. So I'm looking forward to have Harry reveal his sources and we'll probably find out that it's the White House."
Reid's Thursday statement revived a criticism that Romney has not followed through on a promise he made to an ABC News reporter "that he would check his tax returns and let the American people know whether he ever paid a rate lower than 13.9 percent. One day later, his campaign raced to say he had no intention of putting out any further information.
"It's clear Romney is hiding something, and the American people deserve to know what it is," Reid said. "Whatever Romney's hiding probably speaks volumes about how he would approach issues that directly impact middle-class families, like tax reform and the economy. When you are running for president, you should be an open book."
In a conference call Wednesday with Nevada reporters, Reid said the burden of proof is on Romney to show he paid taxes.
A spokesman for Reid said Thursday Reid "stands by his comments," CNN reported.
"Governor Romney's continued refusal to release his tax returns raises legitimate questions about what he is hiding and whether he paid any taxes at all," spokesman Adam Jentleson said. "Governor Romney can easily end this debate by following the precedent set by his father and releasing his tax returns."
Romney has released his 2010 return, filed in 2011, and has said he will release his return for last year. But the candidate, whose father, the late George Romney, pioneered the political practice of financial disclosure, has refused to release older returns.
Eric Fehrnstrom, a Romney spokesman, said in an appearance on Fox News Reid's charge about Romney not paying taxes is "baseless" and "untrue." Romney has said he has always obeyed the law in his tax filings.