A student who tracks the private jets of celebrities says Taylor Swift's lawyers have threatened to sue him for sharing her flight information online.
Jack Sweeney uses publicly available data to track the take-offs and landings of planes belonging to the wealthy and posts them one day later.
The tracking amounts to "stalking", Swift's lawyers claim.
In 2022, Twitter banned Mr Sweeney after Elon Musk accused him of sharing his "assassination coordinates".
Swift's lawyers have issued a cease-and-desist letter to Mr Sweeney, a 21-year-old student at the University of Central Florida, demanding that he stop sharing the location of her private jet.
The letter, issued in December, says that the information poses "an imminent threat to the safety and wellbeing" of Swift, calling it a "life-or-death matter" for her.
It cites numerous stalkers she has dealt with in her career, and says the data gives criminals "a roadmap to carry out their plans".
The BBC has not independently reviewed the letter, whose contents have been reported by US media.
In a statement to the BBC, Mr Sweeney said "nowhere do I intend for harm".
"I actually think Swift has some good songs. I believe in transparency and public information, " he said.
He added that he received the threatening letter after media outlets began scrutinising Swift's carbon footprint.
In 2022, Swift topped the list of celebrities with the highest private jet CO2 emissions, according to digital marketing firm Yard.
The organisation found that her jet emissions were about 1,185 times more than the average person's total annual emissions.
Last month, a 33-year-old man was arrested on stalking charges outside the singer's home.
A spokeswoman for Taylor Swift told US media that the posts about her jet were partly to blame.
"We cannot comment on any ongoing police investigation but can confirm the timing of stalkers suggests a connection," said spokeswoman Tree Paine.
"His posts tell you exactly when and where she would be."
The BBC has contacted Swift's lawyers for comment.
Her travel plans have also drawn increased attention from fans in recent months due to her highly publicised concert tour.
On Sunday, she is due to fly to Las Vegas to see her boyfriend play in the NFL Super Bowl, one day after her concert in Tokyo.
Mr Sweeney's posts do not provide any information about who is traveling on the planes, or where the travellers go once they land.
He has also tracked the private flights of other wealthy Americans, including Microsoft co-founder Bill Gates, Amazon founder Jeff Bezos, and Meta chief executive Mark Zuckerberg.
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