Hillary Clinton is facing renewed calls for FBI – as well as IRS and FTC – investigations even after she tried to close the book on her email scandal ahead of her party convention this week in Philadelphia, this time over questions about the tangled dealings of her family’s Clinton Foundation.

A group of 64 House Republicans, in a letter, has asked the FBI, the Internal Revenue Service and the Federal Trade Commission to examine the dealings of the foundation, alleging “criminal conduct” and describing it as a “pay to play” enterprise.

“I don’t know if it would be a super PAC or a for-profit entity,” Rep. Marsha Blackburn, R-Tenn., who circulated the letter, told FoxNews.com. “There sure is a lot of money going through there and it seems the contributions would touch on Bill Clinton, Hillary Clinton and the Clinton Foundation. It is a hub of some kind of activity and let’s leave it to the IRS, the FBI and the FTC to discern exactly what that is.”

The letter, sent July 15 though not widely reported at the time, focuses primarily on three unresolved controversies, brought up by Peter Schweizer’s book, “Clinton Cash” and New York Times reporting in 2015. They involve the inconsistencies with the foundation’s initial 501(c)(3) filing; the sale of a company called Uranium One; and the Clintons’ ties with Laureate International Universities, a for-profit education company.

“The foundation has routinely gone behind its pledge to act in furtherance of charitable causes and beyond that scope of activities indicated in its initial filings with the IRS,” the letter says. “The appearance of ‘pay to play’ transactions involving Laureate and Uranium One also raise serious allegations of criminal conduct requiring further explanation.”

The Clinton Foundation press office did not respond to numerous phone and email inquiries from FoxNews.com.

However, Hillary Clinton’s presidential campaign blasted the members for seeking an additional probe.

“This is another baseless political attack from House Republicans who just spent two years and $7 million of taxpayer money on the sham Benghazi Committee and are now just regurgitating the debunked claims from the widely discredited book ‘Clinton Cash,’” Clinton campaign spokesman Josh Schwerin told FoxNews.com in a statement.

That’s a predictable response anytime a controversy comes up about the Clintons, Blackburn said.

“They always say that something is old news or that it is a right-wing conspiracy,” Blackburn said. “It’s not a right-wing conspiracy. This is about the rule of law and many times the Clintons feel like they can skirt having closer inspection of their activities by claiming that it is a conspiracy.”

The letter goes on to make a comparison to the indictment of a congressional colleague, Rep. Corrine Brown, D-Fla., on fraud charges regarding her nonprofit.

“The Justice Department indicted a member of Congress for soliciting over $800,000 for charitable cases which were used ‘as a personal slush fund,’” the letter says. “The Clinton Foundation collected $337,985,726.00 in contributions, grants and other revenue in 2014 alone.”

The letter details how former President Bill Clinton accepted $16.5 million as honorary chancellor at Laureate International Universities, founded by Douglas Becker. The company also gave between $1 million and $5 million to the Clinton Foundation. Bloomberg News reported the U.S. Agency for International Development, an appendage of the State Department, gave more than $55 million to Becker’s International Youth Foundation, while Hillary Clinton was the secretary of state.

A Laureate spokesperson pushed back, telling FoxNews.com, “Allegations of any quid pro quo between Laureate, the International Youth Foundation and the Clintons are completely false. … IYF and Laureate Education are independent organizations. Laureate has never received any funds from IYF.” The spokesperson pointed to PolitiFact and Washington Post Fact Checker articles on the issue, while IYF CEO William Reese stated in an open letter that Becker was the board chairman, but the organization has received State Department funding since 1999.

On another front, Uranium One Chairman Ian Telfer donated a total of $2.35 million to the foundation – and the New York Times reported that former President Clinton once received $500,000 for a speech in Moscow from a company promoting Uranium One stock. As secretary of state, Hillary Clinton was among the U.S. officials that approved the Uranium One sale to Russian investors.

Uranium One did not respond to phone and email inquiries. However, citing a complex timeline, PolitiFact ranked the accusation of a quid pro quo as “mostly false.” The fact checks on both companies relate only to past comments by Donald Trump and not the House Republicans' letter.

The foundation’s website suggests contributors do not receive anything in return aside from the knowledge they are making a difference.

The FBI has stayed curiously mum on the subject, though, even after closing the email investigation with no charges filed. During testimony before the House Oversight and Government Reform Committee, FBI Director James Comey responded, “I’m not going to comment on the existence or nonexistence of other investigations,” when asked if the bureau was investigating the Clinton Foundation.

Matthew Whitaker, a former U.S. attorney for the Southern District of Iowa, said the information warrants a federal investigation into the Uranium One deal. However, he thinks the for-profit university issue could be murkier.

“It appears to me there was a conflict of interest with Uranium One,” Whitaker, the executive director of the government watchdog group Foundation for Accountability and Civic Trust, told FoxNews.com. “There are a lot of fringe transactions surrounding Bill Clinton and the Clinton Foundation.”

As for the questions over the 501(c)(3) filing, the tax filing for the organization from December 1997 described the organization as running a presidential library, maintaining archives and doing research.

“No mention is made of conducting activities outside of the United States, which is one of the codes included in the IRS ‘Application for Recognition of Exemption’ in effect at that time,” the letter says. “As a result, the Foundation’s global initiatives appear to be unlawful pursuant to the IRS code.”

Last year, Blackburn asked the IRS to investigate about whether the foundation is adhering to its stated mission when filing tax exempt forms. IRS Commissioner John Koskinen wrote her stating the agency “will consider the information.”

Earlier this year, she and other members asked the FTC to investigate potential fraud, saying just 15 percent of contributions go to “direct programs and expenditures.” However, FTC Chairwoman Edith Ramirez responded there was not enough evidence to prompt an investigation.

The Clinton Foundation is not rated on the FTC’s “Charity Navigator,” as most other nonprofits are. This raised many red flags for members, Blackburn said.

The Clinton Foundation explains on its website:

“Charity Navigator maintains that their placement of foundation on their watch list was due to rating methodology, and ‘is neither a condemnation nor endorsement of this charity.’ … Other organizations who rate financial performance and oversight such as The American Institute of Philanthropy’s ‘Charity Watch’ awarded the Clinton Foundation an ‘A’ rating for its financial performance, noting that the Foundation spent 89 percent of its 2013 expenses on charitable programs and activities.”