A libertarian organization that paid for plane tickets and other expenses for Rep. Ron Paul says after an audit that the Texas Republican defrauded the group for about $20,000. The group is pushing Paul for repayment and exploring legal remedies.

The Liberty Committee, a nonprofit headed by former Paul aide David James, said in an April 16 letter that about two-thirds of the 63 airline tickets the group reimbursed Paul for were also paid for by taxpayers.

“In short, this practice of double or duplicate billing enriched you while draining funds intended for legitimate projects,” the letter read.

Paul spokesman Jesse Benton said James, who worked for Paul for 18 years and says he still supports the lawmaker’s political message, is “pursuing a personal grudge” against the Texas Republican. Benton said Paul will be “happy” to review the allegations.

Paul announced today that he was suspending active campaigning in the GOP presidential race but will continue to campaign for delegates at state conventions.

As reported by Roll Call in February, Paul was paid twice on several occasions for flights between Washington, D.C., and his Congressional district, receiving reimbursement from taxpayers and also from a network of political and nonprofit organizations he controlled, according to public records and Paul’s credit card statements.

Handwritten notations on credit card statements indicate Paul billed the Liberty Committee, his campaign, his political action committee and another nonprofit, the Foundation for Rational Economics and Education, for plane tickets and other expenses for which he also billed taxpayers.

In all, Roll Call found 26 flights from 1998 to 2005 for which several layers of documentation show double payments.

But the Liberty Committee audit revealed a new set of flights that it said were reimbursed twice, bringing the total number of such instances to 52.

James said the Liberty Committee is exploring legal options to press for repayment in court, including researching whether the statute of limitations has expired.

Melanie Sloan, the president of Citizens for Responsibility and Ethics in Washington, said the House Ethics Committee should investigate.

Although the double-billed flights from 1998 to 2005 “fall outside of the Ethics Committee’s statute of limitations, given the long-standing pattern of behavior, the Ethics Committee should investigate on its own as to whether Paul continued this conduct in more recent years,” Sloan said.

The April 16 Liberty Committee letter demanded repayment within 10 business days. Paul responded in an April 26 letter, writing,  “My records do not show any mistaken reimbursements, but I do take these matters very seriously. Please send me copies of all the record [sic] you refer to — invoices, receipts and tickets — and I will have my staff review them thoroughly to determine if any mistakes were in fact made.”

On Saturday, Benton said that James “has not sent any records or documentation of any kind to back up his claims of decade-old double reimbursement, only a letter demanding $20,000.”

James said he attached a chart documenting the results of the group’s audit with the April 16 letter.

Roll Call sent the chart, which includes the purchase dates and itinerary for the plane tickets, the check numbers for the Liberty Committee payments and the volume and page number of the statement of disbursement listings of the taxpayer payments for those flights, to Benton but did not receive further reply from the spokesman.

James discovered a single instance of a double-billed flight in 2005. Thinking it was accidental, he faxed a letter to Paul’s office, requesting that the group’s money be returned for the flight. Paul repaid the $403.70, but the episode strained his relationship with the Liberty Committee and led to a falling out a year later.

In a subsequent conversation, James raised the issue and Paul “was very curt, and he simply said, ‘Yep, well, happens all the time,’” James said.

Paul’s campaign has declined requests to make the Congressman available for an interview.

In a hallway of the Rayburn House Office Building in late February, Paul declined to answer questions about the matter.

Like other businesses, Members of Congress submit receipts for expenses to the House of Representatives administrative office for reimbursement. A source familiar with the process said these receipts are reviewed by House auditors and routine errors are found and corrected but that the office has no capacity to investigate whether a PAC or other entity is reimbursing Members for the same expenses.

Those expenses are listed in a quarterly statement of disbursements published by the Chief Administrative Officer of the House.

In 2009, the House released its quarterly expense reports online for the first time. But Congressional administrators erased a vast array of details on the expenditures, making it impossible to determine what much of the money was spent on.

The post-2009 House records offer almost no details. Expenses are described as “commercial transportation” or “travel subsistence.” In many cases, the amounts itemized are large enough to suggest numerous expenses are being grouped together on the same line item, obscuring the costs of individual purchases.

The changes make it almost impossible to track whether Members are being paid by taxpayers and other groups for the same items.

Since the Paul story broke, Rep. Mike Quigley (D-Ill.) has introduced a resolution to strengthen travel reporting requirements in the House.

Quigley’s proposal would require Members to itemize individual travel expenses, among other things, in order to fill in gaps in publicly reported data that arose in 2009.

Salley Wood, a spokeswoman for House Administration Chairman Dan Lungren (R-Calif.), said Lungren is reviewing Quigley’s proposal.