The DOJ wrote the warning letter to Musk’s organization sometime in the last few days, according to CNN. The revelation came after the tech billionaire announced on Saturday while stumping for Trump at an event in Pennsylvania that he would give away $1 million to random voters who signed his super PAC’s petition in support of constitutional freedoms.

“We want to try to get over a million, maybe two million voters in the battleground states to sign the petition in support of the First and Second Amendment,” Musk said on Saturday. “We are going to be awarding $1 million randomly to people who have signed the petition every day from now until the election.”

The move by Musk was met with immediate concerns from legal experts, who noted that it is against federal law to pay someone to vote or to register to vote. Musk’s giveaway, they noted, was advertised to registered voters, though the process of signing the petition does not appear to check for voter registration status.

Musk offered the giveaway to voters in seven swing states only, a point that David Becker, executive director of the Center for Election and Innovation Research, said would help prosecutors if they wanted to press charges against Musk.

“It’s designed to only affect political outcomes in seven states. Voters in California, voters in Texas are not eligible for this promotion,” Becker told reporters on a call this week. “This is not a particularly close call.”

Becker, a former DOJ trial attorney who specialized in voting law, added that “the facts are not good for Mr. Musk.”

 “If this was only for data collection and it wasn’t intended to influence the outcome of the election, why only the seven swing states? Why was this done in Pennsylvania right before the registration deadline?” he asked.

Musk has thus far given away $1 million to three different recipients. He announced his most recent winner, Andy from North Carolina, on Tuesday night.

If Musk is unresponsive to the DOJ’s letter, the DOJ could escalate matters. A legal fight could ensue, and recipients of the million-dollar prizes could end up being forced to return their winnings.

An email associated with Musk’s super PAC did not return a request for comment, and neither did the DOJ.