JUST IN: The Justice Department has sent a letter to Elon Musk’s super PAC warning that its $1 million daily giveaway in swing states could be illegal, a source says.

The Justice Department has sent a letter to tech billionaire Elon Musk’s super PAC, America PAC, warning that its $1 million daily giveaway in battleground states may run afoul of federal law, a source familiar with the matter said.

The letter, which was reported earlier by CNN, came from the department’s Public Integrity Section, the source said. That section handles election-related prosecutions and related cases.

The Justice Department declined to comment, and the super PAC’s treasurer did not immediately reply to a voicemail message requesting comment.

Pressure has been mounting on state and federal authorities to investigate Musk’s lottery as a potential violation of election laws, including a ban on paying people to register to vote. On Monday, a group of ex-prosecutors and other former government officials sent a letter to the Justice Department requesting an investigation.

It’s unclear when the letter went out or what further action, if any, the Justice Department might take.

Legal experts have told NBC News that they believe Musk’s contest falls into a legal gray area and could violate election law, but not necessarily.

“I can see what people are saying when they argue this violates the law, but I don’t think it does,” said Matthew Sanderson, an election law expert who has worked with Republicans and is an NBC News consultant.

On Tuesday, A source familiar with the efforts of America PAC said, “The PAC is confident in the legality of this initiative.”

Federal law prohibits paying people to register to vote. The daily drawing by America PAC has two requirements to enter, according to the contest website: be a registered voter in one of seven swing states and sign a petition supporting the First and Second amendments.

“Our goal is to get 1 million registered voters in swing states to sign in support of the Constitution, especially freedom of speech and the right to bear arms,” it says.

Musk has also mentioned a third requirement to win: “be a spokesperson for the petition” in support of speech rights and gun rights. So far, several of the winners have appeared in short videos for America PAC talking about their support for former President Donald Trump.

The contest is open to those in Arizona, Georgia, Michigan, Nevada, North Carolina, Pennsylvania and Wisconsin.

Musk, who has endorsed Trump’s campaign, launched America PAC in an effort to help elect him. Last week, Musk appeared several times in Pennsylvania to encourage last-minute voter registration. At the events, he repeatedly praised Trump and echoed various conspiracy theories.

Musk announced the daily giveaway Saturday at a town hall event in Harrisburg, Pennsylvania, saying he would give away $1 million a day until Election Day. Four winners have been named so far.

Musk, the CEO of Tesla and SpaceX, is the world’s wealthiest person, with a net worth of $240 billion, according to the Bloomberg Billionaires Index.