Melania Trump is suing a British newspaper and a US blogger for $150m (£114m) over allegations she was a sex worker in the 1990s, her lawyer says.
The Daily Mail suggested Mrs Trump may have worked as a part-time escort in New York, and met husband Donald Trump, who is now running for the White House, earlier than previously reported.
The claims were "outright lying", lawyer Charles Harder said.
Both the blogger and the Daily Mail have since retracted their articles.
"These defendants made several statements about Mrs Trump that are 100% false and tremendously damaging to her personal and professional reputation," Mr Harder said in a statement.
"Defendants' actions are so egregious, malicious and harmful to Mrs Trump that her damages are estimated at $150m," Mr Harder's statement said.
He has filed the complaint before the Circuit Court for Montgomery County in the US state of Maryland.
The document states that Melania Trump asks the court to rule against all defendants "in an amount in excess of Seventy Five Thousand Dollars ($75,000) in compensatory and punitive damages".
There has been no explanation of the discrepancy.
Mrs Trump, 46, was born in Slovenia and moved to the US to work as a model in the 1990s. She married Mr Trump in 2005.
What are her chances of winning? - By Clive Coleman, BBC legal affairs correspondent
For Melania Trump to succeed in a defamation action in the US she would have to prove that the Daily Mail acted maliciously.
In other words, she would have to provide evidence that the British newspaper was aware that the allegations were false and yet went on ‒ deliberately and maliciously ‒ to publish them.
That would be a very difficult task, especially as it is clear that the paper had sources for the story. So the chances of a successful claim in the US are remote.
However, the position would be different if Mrs Trump sued here. She clearly has a reputation in the UK ‒ she is a global figure and is entitled to bring a claim.
If she could prove that the published allegations were defamatory and that she had suffered serious harm as a result, it would be hard for the Daily Mail to defend an action. Also, in light of its retraction it could not argue that it was justified in publishing.
The big difference is that the maximum damages for a defamation claim here would be about £300,000 ‒ a fraction of the $150m (£112m) Mrs Trump's lawyers say the claim is worth.
In July, Mrs Trump was embroiled in a row over plagiarism, after her speech at the Republican convention. Lines matched almost word for word those delivered by First Lady Michelle Obama at the Democrats' convention in 2008.
An employee of the Trump Organisation, Meredith McIver, later admitted her role in writing the speech, saying it was her mistake.