"I think he should release his taxes," Duffy told CNN's Wolf Blitzer on "The Situation Room." "I think he should. I think Hillary Clinton should also release her emails. She should also release the donors to the Clinton Foundation. I think transparency in government is the best."
Duffy -- who supported Florida Sen. Marco Rubio during the primaries and now backs Trump, the Republican presidential nominee -- told Blitzer that he thinks both candidates should release the information so voters can make educated decisions at the polls in November.
Blitzer noted that Clinton Foundation has released its list of donors
, and asked whether Duffy was referring to transcripts of Clinton's speeches on Wall Street -- which the former secretary of state has not released.
Duffy replied that "all of the donors have not been released." He added that he would also like to see the transcripts of Clinton's speeches.
"We deserve all the information about these candidates that we can get our hands on to make an educated vote in November," he told Blitzer.
Trump said in May he would make his tax returns public when the "routine audit" they are under is complete, though the IRS has said there is nothing legally keeping him from releasing them while they under review.
"In interview I told @AP that my taxes are under routine audit and I would release my tax returns when audit is complete, not after election!" the real estate mogul tweeted.
And Trump's campaign chairman Paul Manafort has said he doesn't think the Republican nominee will release his returns -- saying the documents are "incredibly complicated" and the American people wouldn't understand them.
"The only people who want the tax returns are the people who want to defeat him," Manafort said.
The GOP's 2012 nominee, Mitt Romney, has called Trump's decision not to release his returns "disqualifying."
"Mr. Trump says he is being audited," Romney wrote in a Facebook post
in May. "So? There is nothing that prevents releasing tax returns that are being audited. Further, he could release returns for the years immediately prior to the years under audit."
Romney, who has been a vocal critic of Trump, said there was "only one logical explanation" for Trump's refusal to release his returns: "There is a bombshell in them."