A New York Times article in 2018 alleged Mr Trump had "participated in dubious tax schemes" in the 1990s
Former US President Donald Trump is suing his niece and the New York Times over a 2018 article that alleged he was involved in "dubious tax schemes".
It alleges that Ms Trump, 56, breached a settlement agreement barring her from disclosing the documents.
She revealed herself as the source of the story in a tell-all memoir in 2020.
Ms Trump, the daughter of Fred Trump Jr, the president's older brother who died in 1981 at the age of 42, has not yet commented on the lawsuit.
Mr Trump has consistently rejected the claims made in his niece's book - Too Much and Never Enough: How My Family Created the World's Most Dangerous Man - and unsuccessfully sued to try to block its publication.
On Tuesday, a lawsuit filed in a state court accused New York Times journalists Susanne Craig, David Barstow and Russell Buettner of contacting and working with Mr Trump's niece as part of a "personal vendetta" against him.
It alleges that Mr Trump "suffered significant damages" and states that he is seeking compensation of no less than $100m (£73m).
In her book, Ms Trump describes how she supplied tax documents to the New York Times, which were used to form part of a 14,000 word investigative article into Mr Trump's "dubious tax schemes during the 1990s, including instances of outright fraud, that greatly increased the fortune he received from his parents".
One of the reporters named in the lawsuit, Ms Craig, tweeted in response to the allegations: "I knocked on Mary Trump's door. She opened it. I think they call that journalism."
A New York Times spokeswoman, Danielle Rhoades Ha, said the newspaper's coverage of Mr Trump's taxes "helped inform citizens through meticulous reporting on a subject of overriding public interest", and that the lawsuit was "an attempt to silence independent news organisations".
Last year, Ms Trump filed her own lawsuit accusing Mr Trump and two family members of fraud and conspiracy, alleging that the then-president, his sister Maryanne Trump Barry and brother Robert Trump - who died last August - cheated her out of an inheritance.
That case is still pending.