A campaign finance watchdog has filed a complaint with the Federal Election Commission alleging Pete Buttigieg’s campaign illegally coordinated advertising with a super PAC.

VoteVets, a super PAC that supports military veterans in politics and has thrown its support behind Buttigieg, bought more than $630,000 in television advertising in Nevada — a move that came one week after Buttigieg campaign strategist Michael Halle tweeted that the former South Bend, Indiana, mayor would benefit from his military record being on the airwaves in Nevada through the caucuses, which are on Feb. 22.

The nonpartisan Campaign Legal Center, which works to lessen the influence of money in politics, said in its complaint filed Tuesday that “there is reason to believe that VoteVets made, and the Buttigieg campaign accepted, over $639,000 in illegal and excessive in-kind contributions in the form of coordinated communications.”

HuffPost reported on the tweet and the subsequent VoteVet ads, noting that Halle’s tweet did not appear to violate anti-coordination laws because he sent it in a public forum for all to see. However the Campaign Legal Center says the specificity of the tweet makes it worthy of more legal scrutiny.

“The tweet was very concise, but it was also very specific,” said Brendan Fischer, a campaign finance expert with CLC. “The campaign acknowledged VoteVets was the audience for this communication. The level of specificity for the tweet and the clear audience for the tweet requested and suggested VoteVets run these ads — and then they did.”

CLC’s use of “requested” or “suggested” is crucial to its complaint. While federal anti-coordination law does allow exceptions “if the information material to the creation, production, or distribution of the communication was obtained from a publicly available source,” that exception does not apply if the campaign is directly suggesting or requesting specific content.

The Buttigieg campaign declined to comment.

On Feb. 5, Halle tweeted: “Pete’s military experience and closing message from Iowa work everywhere especially in Nevada where it’s critical they see this on the air through the caucus.”

The Buttigieg campaign did not deny that VoteVets was the audience for the tweet. Chris Meagher, a Buttigieg spokesman, said that “if the largest progressive veterans group wants to help spread the word about his service, we welcome it,” in a statement to Politico.

The following week, VoteVets ran television advertising in Nevada doing just that.

If the FEC does find the Buttigieg campaign in violation of the law, it would likely result in a fine, Fischer said. He added that the elections commission rules were written decades ago, before the widespread use of social media in presidential campaigns, which can make implementation fuzzy.

“There’s a fair argument that the FEC coordination rules are so lax and so underenforced that this kind of coordination is legal,” Fischer said. “It’s certainly the case that the FEC has failed to enforce the coordination rules that are on the books, and that invites super PACs and parties to push the legal bounds.”

But he noted, when it comes to “requesting or suggesting” advertising, the FEC is explicit: There’s no exception for public forums.

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This article originally appeared on HuffPost.