First lady Melania Trump is threatening a $1 billion defamation suit against Hunter Biden over a claim that she was introduced to President Trump by disgraced financier Jeffrey Epstein.

In a tactic reminiscent of legal actions initiated by her husband — most recently against the Wall Street Journal and its owner, Rupert Murdoch — Mrs. Trump charges that the son of President Biden has done overwhelming harm to her reputation with the “extremely salacious” claim.

A Florida-based attorney, Alejandro Brito, sent a letter to Mr. Biden and his attorney, Abbe Lowell, last week demanding that he retract comments he made in an interview with an independent journalist, Andrew Callaghan.

“These false, disparaging, defamatory, and inflammatory statements are extremely salacious and have been widely disseminated throughout various digital mediums,” Mr. Brito writes in the letter.

He demands that Mr. Biden “immediately retract” the statements, which were posted last week on the journalist’s YouTube channel, “Channel 5 with Andrew Callaghan,” or face legal action seeking more than $1 billion in damages.

The letter also tells Mr. Biden that “you lack any viable defense to the overwhelming reputational and financial harm you have caused Mrs. Trump to suffer.”

Mr. Biden returned to “Channel 5” to address the letter in a video that was posted Thursday morning.

“So now, we’re here maybe to give you the platform to apologize to the first lady for your statements that you made about her possible connection to Jeffrey Epstein,” Mr. Callaghan said as he introduced his guest.

“Uh … f— that. That’s not going to happen,” Mr. Biden replied, followed by a defiant chuckle.

He continued: “Well, first of all is that what I said was what I have heard and seen reported and written primarily from Michael Wolff, but also dating back all the way to 2019 when the New York Times, I think Annie Karni and Maggie Haberman, reported that sources said that Jeffrey Epstein claimed to be the person to introduce Donald Trump to Melania at that time.”

Mrs. Trump’s lawyer also identified “serial fabulist” Michael Wolff as the primary source for the Mr. Biden’s claim, based on an article for the Daily Beast under the headline, “Melania Trump ‘Very Involved’ in Epstein Scandal: Author.”

“Following receipt of our cease-and-desist demand letter just a week ago, The Daily Beast issued an apology to Mrs. Trump and retracted the false and defamatory statements contained in the article by deleting it in its entirety,” Mr. Brito said in the letter.

“Despite this, you have unjustifiably relied upon Mr. Wolff’s false, defamatory, disparaging, and inflammatory statements about Mrs. Trump and maliciously elected to republish them.”

The August 6 letter gave Mr. Biden just 24 hours to respond and take appropriate action, but the lawsuit has yet to be filed.

Mr. Brito did not immediately respond to a request for comment.

Mr. Biden also claimed in his most recent interview that if the lawsuit is carried forward, both President Trump and the first lady would have to sit for depositions.

“I think the entire world would love to finally get to the bottom of the true nature of their relationship.”