Up to 4,000 people voting overseas in the US election are having their ballots challenged in Pennsylvania, a key battleground state, according to the American Civil Liberties Union (ACLU).
They include Selma Aldi, 47, from Camden in north London who received a letter on Sunday explaining that her ballot in the US presidential election is at risk of being rejected.
"It was a shock," she said. "It was terrifying to be targeted, to potentially lose a right that I hold as very important. It's even a feeling that someone is questioning my identity."
Latest on US election
The trainee GP, who grew up in Hershey, Pennsylvania left America in 2000 but has voted via absentee ballot in every US presidential election since.
A letter from election officials in Dauphin County outlines the legal challenge. It reads: "The applicant is not registered to vote and therefore is not eligible to vote in Pennsylvania.
"Under Pennsylvania law, it is a felony to permit any person to vote who is not registered."
A hearing on the legal challenge is scheduled for Friday, in which Ms Aldi can respond.
Around 2.8 million US citizens living abroad are entitled to vote in the election, no matter where they are on polling day.
But each state has different procedures and rules on how election paperwork can be sent and received.
But Ari Savitzky, senior staff Attorney at the ACLU said "any attempt to challenge [voters] eligibility is a clear violation of their rights".
He told Sky News: "Between 3,000 and 4,000 challenges have been filed in Pennsylvania to the absentee ballots of US citizens living abroad.
"For decades, federal law has guaranteed the right of US citizens living abroad to vote in federal elections at their last US residence.
"In addition to being legally baseless, these challenges are an abuse to voters and to election administrators."
Read more from Sky News:
US election: Colleges, swing states and how it all works
Should we fear Trumponomics?
What happens if there's a tie in the US election?
Deborah Hinchey from another voting rights group, All Voting is Local, said: "Election deniers across Pennsylvania have submitted thousands of mass challenges to overseas voters.
"They want to block as many ballots as possible and silence our voices... but these baseless challenges have failed before and the proper checks and balances are in place to make sure they'll fail again," she added.
Predict who you think will win in each swing state and we'll tell you who the president will be if you're right.
Tonight, Sky News will have access to the most comprehensive exit poll and vote-counting results from every state, county and demographic across America through its US-partner network NBC.
You can find out more about Sky News' coverage here.
(c) Sky News 2024: Voter in UK 'terrified' by US election legal battle, as up to 4,000 ballots challenged in P
As 18% of Brits want Trump to win - how much of an impact will US election winner have on UK?
Suspicious parcel fire at Birmingham warehouse was 'test run' by Russian spies ahead of US attack
Amy Dowden 'heartbroken' as she leaves this year's Strictly Come Dancing
CCTV shows predator lure victim into car - with friends rescuing her when she shares location
Elon Musk can keep giving away $1m to voters, judge rules - as lawyer admits winners aren't chosen randomly
Island Planning Strategy Submitted To Secretary Of State
Southern Water Unveils Plans For New Water Recycling Plant On Isle Of Wight
Campaign Group Condemns Wootton Bridge Palmers Farm Plans
Yacht Fire Leads To Cowes RNLI Lifeboat Launching