Tech billionaire Elon Musk has said he will give away $1m (£766,000) a day to a registered voter in key swing states until the US presidential election on 5 November.

The winner will be chosen at random from those who sign a pro-US Constitution petition by Mr Musk’s campaign group AmericaPAC, which he set up to support Republican nominee Donald Trump’s bid to return to the White House.

The first lottery-style cheque was given away to a surprised attendee at a town hall event in Pennsylvania on Saturday night. Another cheque was handed out on Sunday.

Pennsylvania Governor Josh Shapiro, a Democrat who supports Kamala Harris, called Mr Musk’s strategy “deeply concerning.”

“Who can sign the petitions? Only registered voters in swing states, which is what makes it illegal,” said Mr Hasen, a professor at the University of California, Los Angeles (UCLA) law school.

Those who sign the petition – which pledges to support free speech and gun rights – must submit their contact details, potentially allowing AmericaPAC to contact them about their vote.

Both Mr Musk and AmericaPAC have been approached for comment.

Campaigns and political action committees rely on tactics like petition signing, survey requests, or merchandise purchases to build massive databases of voter information. That data can then be used more accurately to target voters, or raise funds from supporters who are already onboard.

In Pennsylvania, Mr Musk is giving voters $100 for signing the petition, plus another $100 for each person they refer who signs. Voters in other battleground states get $47 per referral.

But the strategy may be covered by a loophole under US election law because no-one is being directly paid to vote – despite introducing money into a process that could identify likely Trump voters.

In the US, it is illegal to provide payments to get people to vote – not only for a certain candidate but to simply cast a ballot.

The rule prompted ice cream maker Ben & Jerry’s to give its product free to everyone on election day in 2008, having initially planned to limit it just to those with an “I voted” sticker.

While campaigning on Sunday, Trump was asked about Mr Musk’s giveaway.

“I haven’t followed that,” he said, adding that he speaks to Mr Musk often and he is a “friend”.

The founder of SpaceX and Tesla and owner of X, formerly Twitter, has emerged as a key Trump supporter.

Mr Musk launched AmericaPAC in July with the aim of supporting the former president’s campaign.

He has so far donated $75m (£57.5m) to the group, which has quickly become a central player in Trump’s election bid.

The Trump campaign is highly reliant on outside groups such as AmericaPAC to canvas voters.

A statement on the group’s website reads: “AmericaPAC was created to support these key values: Secure Borders, Safe Cities, Sensible spending, Fair Justice System, Free Speech, Right to Self-Protection.”

Mr Musk said he wants 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”.

“I think [it] sends a crucial message to our elected politicians,” he added.

Mr Musk is currently the world’s richest man, with an estimated net worth of $248bn (£191bn), according to US business magazine Forbes.