One of Bernie Sanders’ campaign features has been his eschewing of big donors, especially those on Wall Street.  He’s been quite vocal about his pride in collecting only small donations from the grassroots and damning the “corrupt campaign finance system.”

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The Federal Election Commission, however, has flagged thousands of illegal donations to the Sanders campaign, including those from people donating over the limit and those from foreign nationals.

The Washington Free Beacon reports:

Thousands of contributions to Democratic presidential candidate Bernie Sanders’ campaign in January violated federal campaign finance laws, election regulators said on Thursday.

The Federal Election Commission sent a letter to the Democratic presidential candidate’s campaign committee on Thursday with a 90-page spreadsheet listing 3,457 “excessive, prohibited, and impermissible contributions.”

The campaign’s January financial disclosure filing listed contributions from foreign nationals and unregistered political committees, the FEC said. Other contributions came from donors who exceeded the $2,700 per-election limit.

The FEC suggests that further legal action may take place, though Bernie’s refunding of these illegally-obtained monies “will be taken into consideration.”

The Washington Free Beacon continues:

“Although the Commission may take further legal action concerning the acceptance of [excessive or prohibited] contributions, your prompt action to refund the prohibited amount will be taken into consideration,” the FEC told the campaign.

Sanders’ campaign has relied on small-dollar individual contributions to a far greater extent than any other presidential campaign, including the Super PAC- and dark money-fueled efforts of Democratic rival Hillary Clinton.

This is not the first time that Bernie has been warned about illegal donations and problematic record-keeping.

The FEC sent a letter to the Sanders campaign earlier this month flagging an additional 1,316 “excessive, prohibited, and impermissible contributions” in the fourth quarter of 2015.

The commission also noted disbursements from the campaign that failed to include required documentation.

Additionally, foreign nationals are donating their “small” (and illegal) donations over the internet.

Some of the campaign’s legal problems stem from enthusiasm for Sanders’ candidacy from foreign nationals, many of whom have publicly revealed donations to the campaign in violation of U.S. election laws.

“I am German, live in Germany and just donated to Bernie Sanders’ campaign on www.BernieSanders.com simply using my credit card—Is this illegal in any way?” asked a user on the website Quora.

“UPDATE: Donation rescinded based on your answers,” the user later added.

While none of this is likely to deflate Sanders’ supporters’ socialist balloon, it is undoubtedly something that the Hillary campaign will use to rebut Sanders’ repeated attacks on her for her wealthy donors on Wall Street and in corporate America.