Jon Huntsman Sr. urged Mitt Romney on Friday to release more tax returns and said he feels "very badly" that the presumptive Republican presidential nominee "won’t be fair with the American people."

Huntsman, a supporter of Romney's campaign, made the remarks to Greg Sargent at the Washington Post. He said, "I've supported Mitt all along. I wish him well. But I do think he should release his income taxes."

The comments from Huntsman come in the wake of Senate Majority Leader Harry Reid (D-Nev.) saying a Bain investor, who he did not identify by name, told him that Romney "didn't pay any taxes for 10 years." After it was suggested that Huntsman could be Reid's source, Huntsman threw cold water on the speculation in speaking with the Post.

Huntsman stressed, "I have absolutely no knowledge of Bain or Mitt Romney’s tax returns."

In an interview with BusinessWeek published online on Thursday, Romney defended his decision not to release additional tax return documents, saying that he's "not a business."

"We have a process in this country, which was established by law, which provides for the transparency which candidates are required to meet," he said. " I have met with that requirement with full financial disclosure of all my investments, but in addition have provided and will provide a full two years of tax returns."

Nevertheless, Romney has faced mounting pressure on the issue from both sides in recent weeks.

Republican strategist Ed Rollins said last weekend during an appearance on Fox News, "I think at this point of time it's going to dog him all the way and he needs to get it behind him." He added, "I think he needs to release more taxes. Absolutely."

Below, a look at some other Republicans who have called on Romney to release more tax returns.

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  • Ron Paul

    "Politically, I think that would help him," Paul said in a interview with <a href="http://www.politico.com/news/stories/0712/78599.html#ixzz20w7ycTBE" target="_hplink">Politico</a>. "In the scheme of things politically, you know, it looks like releasing tax returns is what the people want."

  • Richard Lugar

    "I have no idea on why he has restricted the number to this point," <a href="http://www.cbsnews.com/8301-18563_162-57474352/pressure-mounts-on-mitt-romney-to-release-more-tax-returns/?tag=socsh" target="_hplink">Lugar said</a>.

  • George Will

    "I don't know why... he didn't get all of this out and tidy up some of his offshore accounts and all the rest," Will said on ABC's "<a href="http://www.huffingtonpost.com/2012/07/15/george-will-mitt-romney-bain_n_1674513.html?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+HP%2FPolitics+(Politics+on+The+Huffington+Post)" target="_hplink">This Week</a>." "He's done nothing illegal, nothing unseemly, nothing improper, but lots that's impolitic."

  • Bill Kristol

    "He should release the tax returns tomorrow. It's crazy," Kristol said on "<a href="http://www.huffingtonpost.com/2012/07/15/mitt-romney-tax-returns_n_1674325.html" target="_hplink">Fox News Sunday</a>." "You gotta release six, eight, 10 years of back tax returns. Take the hit for a day or two."

  • Robert Bentley

    "I just believe in total transparency," Bentley told <a href="http://abcnews.go.com/blogs/politics/2012/07/gop-governor-calls-on-mitt-romney-to-release-additional-tax-returns-and-show-he-has-nothing-to-hide/" target="_hplink">ABC News</a>. "In fact, I was asked today that question -- do you think that Governor Romney should release his tax returns? And I said I do. I said, I release my tax returns. I may be the only public official in Alabama that does, but I release mine every year and I just believe that people should release their tax returns. And if you get them out and just get past that, it just makes it so much easier."

  • Haley Barbour

    When asked on "<a href="http://www.nationaljournal.com/2012-presidential-campaign/barbour-romney-should-release-more-tax-returns-20120710" target="_hplink">The Situation Room</a>" if Romney should release more returns, Barbour said, "I would. But should it be an issue in the campaign? I don't think it amounts to diddly."

  • Michael Steele

    "If there's nothing there, there's no 'there' there, don't create a there,'" Steele said on MSNBC.

  • David Frum

    "Tax returns the next problem. Releasing returns under pressure: more weakness, more pain," Frum <a href="https://twitter.com/davidfrum/status/224509505973661696" target="_hplink">tweeted</a>.