An ethics watchdog is calling on the Federal Election Commission (FEC) to investigate the Maine Democratic Party, alleging that it failed to release funds that were illegally donated to it by 2020 Senate candidate Sara Gideon.

Gideon, who is running to replace Sen. Susan Collins, R-Maine, received reimbursements from her Gideon Leadership PAC after she donated thousands of dollars to both the state's Democratic Party and a congressional campaign -- indicating she violated campaign finance law by serving as a proxy for a PAC's contribution.

According to the Foundation for Accountability and Civic Trust (FACT), the campaign and the party both created additional violations when they failed "refund or disgorge" the contributions within 30 days of learning about them.

“Hiding the source campaign contributions is plainly illegal, and if an organization mistakenly accepts such a contribution it must be refunded. Citizens can only trust in the system of disclosure if honest information is disclosed,” FACT Executive Director Kenda Arnold said in a statement provided to Fox News on Tuesday.

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“Considering the substantial involvement of these two organizations with the donor it is both appropriate and necessary that they be investigated and penalized accordingly."

It pointed to campaign finance reports from both the Maine Democratic Party and Cain for Congress, the campaign arm for former state senator and current Emily's List executive director Emily Cain. The filings appeared to show those entities never released the funds.

The Maine Democratic Party, Emily Cain, Sara Gideon's office and Collins' office didn't immediately respond to Fox News' requests for comment. Nate Brand, press secretary for the National Republican Senatorial Committee, responded with a statement to Fox News.

“Sara Gideon broke the law when she ran a straw donor scheme, and her illegal actions don’t minimize the need for her liberal allies, Cain and the Maine Democrats, to comply with campaign finance laws," Brand said.

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"Gideon’s reliance on questionable donors, illegal straw donor schemes, and dark money special interests should give Mainers pause as she tries to give Maine’s voice away to the liberals in Washington.”

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It's unlikely that those two organizations didn't know about the nature of Gideon's funds given the substantial press coverage of the issue, FACT argued. Gideon and her PAC also notified the organizations of "circumstances" surrounding the contribution, according to FACT's complaint.

"Evidence and Gideon’s own admission demonstrates these contributions were 'straw donations' — they were not from Sara Gideon but from a PAC that commingled impermissible corporate funds."