Huma Abedin and then Secretary of State Hillary Clinton in Zambia in 2011. (Reuters)

State Department investigators concluded this year that Huma Abedin, one of Hillary Rodham Clinton’s closest aides, was overpaid by nearly $10,000 because of violations of rules governing vacation and sick leave during her tenure as an official in the department.

The finding — which Abedin has formally contested — emerged publicly Friday after Sen. Charles E. Grassley (R-Iowa) sent letters to Secretary of State John F. Kerry and others seeking more information about an investigation into possible “criminal” conduct by Abedin concerning her pay.

The letters also sought the status of an inquiry into whether Abedin had violated conflict-of-interest laws related to her special employment situation, which allowed her to work simultaneously for the State Department, the Clinton Foundation and a private firm with close ties to the Clintons.

The finding that Abedin, a longtime Clinton confidante who now serves as vice chairwoman of her presidential campaign, had improperly collected taxpayer money could prove damaging to Clinton’s candidacy, as Republicans charge that government rules were routinely bent to benefit Clinton and her aides.

At the same time, the letters, which for the first time have publicized an internal pay dispute that has been simmering for months, could bolster Democratic claims that congressional Republicans are using their oversight role to hurt Clinton politically.

Democratic presidential candidate Hillary Clinton and Huma Abedin in Lebanon, N.H., on July 3. (Elise Amendola/AP)

Grassley indicates in the letters, which were provided to The Washington Post, that he is describing information from an inquiry by the State Department’s Office of Inspector General. A spokesman for Grassley said the senator’s office has not independently confirmed the allegations.

In letters sent Thursday to Abedin, Kerry and the Office of Inspector General, Grassley wrote that staff of the inspector general had found “at least a reasonable suspicion of a violation” of the law concerning the “theft of public money through time and attendance fraud” as well as “conflicts of interest connected to her overlapping employment.”

Grassley also raised the possibility that efforts to investigate Abedin’s actions were thwarted because many of her exchanges were sent through Clinton’s private e-mail server.

According to Grassley’s description of the investigation, Abedin’s time sheets indicated that she never took vacation or sick leave during her four years at the State Department, from January 2009 to February 2013. But the investigation, the senator wrote, found evidence that Abedin did take time off, including a 10-day trip to Italy, and that she told colleagues in e-mails that she was out “on leave.”

A spokesman for Clinton’s campaign declined to comment. Attorneys for Abedin said she learned in May that the State Department’s inspector general had concluded that she improperly collected $9,857 for periods when she was on vacation or leave.

Abedin responded with a 12-page letter contesting the findings and formally requesting an administrative review of the investigation’s conclusion, a process that remains ongoing.

Her attorneys say the conclusion that Abedin was overpaid relied on a finding that she had done no work while on the Italy trip and in the weeks after she gave birth in December 2011. However, they wrote that the evidence uncovered by the inspector general made it clear that she had worked extensively during those times.

“Huma Abedin is widely known as one of the hardest-working people in all of Washington during the nearly two decades she was in public service,” said Karen Dunn, an attorney for Abedin. “The IG report found a multitude of instances when she was working even when she was on maternity leave, yet its central charge was that she owes back pay for work missed while on leave. It simply doesn’t add up.”

Abedin’s attorneys said the inquiry resulted in a finding only about the pay issue and not about any possible conflicts of interest posed by her work arrangement or issues related to the use of Clinton’s private e-mail server.

Doug Welty, a spokesman for the Office of Inspector General at the State Department, said he couldn’t comment on the existence of a probe into Abedin. A State Department spokesman also declined to comment.

Grassley also alleged that Clinton’s highly controversial private e-mail arrangement interfered with the investigation.

The committee “has learned that the OIG had reason to believe that e-mail evidence relevant to that inquiry was contained in e-mails Ms. Abedin sent and received from her account on Secretary Clinton’s non-government server, making them unavailable to the OIG through its normal statutory right of access to records,” Grassley wrote.

Since 2013, Grassley has been inquiring about Abedin’s “special government employee” status, which during her final six months at the State Department allowed her to take outside employment with the Clinton Foundation and Teneo, a firm led by longtime Bill Clinton aide Douglas Band.

Grassley’s letter to Kerry claimed that Abedin had exchanged 7,300 e-mails that “involved” Band but did not specify how many of those were direct correspondence between the two.

In one instance, Grassley wrote, Band allegedly e-mailed Abedin to request her help in landing a White House appointment for a friend who led a charity that later hired his firm and donated to the Clinton Foundation.

However, Grassley did not release the e-mail in question, nor did he allege any wrongdoing by Abedin. And the timeline of events does not clearly support an allegation of conflict of interest: The Band friend was named to a White House panel in 2010, before her charity hired Teneo and before Teneo hired Abedin.

Band did not respond to requests for comment. Dunn, Abedin’s attorney, said: “We are unaware of this e-mail and Senator Grassley has not shared it with us or the media. But every piece of this letter has issues with accuracy and we have no reason to believe this is an exception.”