Acting Attorney General Matthew G. Whitaker,  gives brief remarks to state and local law enforcement on efforts to combat violent crime and the opioid crisis at the U.S. Courthouse Annex, on November 14, 2018 in Des Moines, Iowa.  Whitaker was appointed as acting attorney general after previous attorney general Jeff Sessions was forced out out of the job. (Photo by Steve Pope/Getty Images)
Steve Pope/Getty Images
Acting Attorney General Matthew G. Whitaker, gives brief remarks to state and local law enforcement on efforts to combat violent crime and the opioid crisis at the U.S. Courthouse Annex, on November 14, 2018 in Des Moines, Iowa. Whitaker was appointed as acting attorney general after previous attorney general Jeff Sessions was forced out out of the job. (Photo by Steve Pope/Getty Images)
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(CNN) —  

An independent federal investigative agency is looking into whether acting Attorney General Matthew Whitaker violated prohibitions on political activities by federal employees by accepting contributions to his 2014 Senate campaign earlier this year.

Last January and February, when Whitaker served as chief of staff at the Department of Justice, four individuals donated a total of $8,800 to the committee for Whitaker’s unsuccessful 2014 run for a Senate seat in Iowa, according to Federal Election Commission records.

RELATED: Whitaker disclosures reveal more than $900,000 in payments from conservative group

Austin Evers, the executive director of the watchdog organization American Oversight, told CNN his group submitted a complaint to the Office of Special Counsel that argued Whitaker may have violated the Hatch Act, which prohibits federal employees from accepting political contributions.

A spokesperson for the Office of Special Counsel confirmed receipt of the complaint and said a case file on the matter has been opened. The office can investigate Hatch Act complaints and recommend discipline but does not directly take disciplinary action. The office has no connection to the Justice Department special counsel’s office that is overseeing Russian interference in the 2016 US election.

The Justice Department declined to comment to CNN. Whitaker did not immediately respond to a request for comment.

According to Office of Special Counsel guidance, “penalties for Hatch Act violations range from reprimand or suspension to removal and debarment from federal employment and may include a civil fine.”

Evers told CNN that questions remain about the purpose and implications of the donations to Whitaker’s campaign.

“After years of being completely dormant and only after he joined Jeff Sessions’ office as chief of staff, Whitaker’s campaign started receiving a cluster of contributions,” Evers said. “It appears to violate the black-letter law of the Hatch Act.”

William Gustoff, a former law partner of Whitaker’s who served as treasurer for Whitaker’s Senate campaign, told CNN that neither he nor Whitaker had solicited the donations made to the campaign earlier this year.

Gustoff said the campaign committee remained open because of remaining debt. FEC records show that Whitaker loaned his campaign $50,000 in 2013, and the committee still owes about $49,000.

When asked about the individuals who made the donations, Gustoff said, “They are all active Republicans who support other candidates in the state of Iowa.”

“They didn’t talk to me and I didn’t talk to them about it,” he added.

Leon Shearer, an Iowa attorney, declined to tell CNN why he had donated $1,000 to Whitaker’s 2014 Senate campaign in January. “I don’t think I have to disclose that,” he said.

The three other contributors could not be reached for comment.

A financial disclosure form released Tuesday showed that Whitaker was paid a total of $904,000 over 2016 and most of 2017 by The Foundation for Accountability and Civic Trust, which received nearly all of its funding from a group called DonorsTrust, whose contributors are mostly anonymous.

Government ethics watchdogs have also raised questions about Whitaker’s earlier political activity.

Internet records reviewed by CNN on Wednesday show Whitaker registered four political website domain names in 2008, when he served as the US attorney in Iowa.

The domains “iowaconservative.us,” “iowaconservative.org,” “iowaconservative.mobi” and “iowaconservative.info” were registered in November 2008 under Whitaker’s name and home address, about a year before he resigned from his position as US attorney.

While the domain names continue to list Whitaker as a registrant, it is unclear if they ever hosted any content.

Sarah Turberville, the director of The Constitution Project at the Project on Government Oversight, said the domain registrations likely do not violate rules for federal employees engaging in political activity since there is no indication that Whitaker used them to support any campaigns, but she said they raised questions about his impartiality as a US attorney.

“There’s a unique trust in the role of the United States attorney,” she said. “When it comes to concerns about the perception of impartiality, this raises a lot of red flags.”