NEW YORK (NYTIMES) - Former US president Donald Trump has filed a lawsuit accusing his niece Mary L. Trump, The New York Times and three of its reporters of conspiring in an "insidious plot" to improperly obtain his confidential tax records and exploit their use in news articles and a book.

The lawsuit claims that the Times reporters, as part of an effort to obtain the tax records, relentlessly sought out Mary Trump, and persuaded her "to smuggle the records out of her attorney's office" and turn them over to the Times.

That action, according to the lawsuit, breached a confidentiality agreement that was part of the settlement of litigation involving the will of the former president's father, Mr Fred C. Trump, who died in 1999.

Mr Donald Trump's lawsuit, filed in state Supreme Court in Dutchess County, New York, accuses the newspaper, its reporters and Ms Mary Trump of being motivated "by a personal vendetta and their desire to gain fame, notoriety, acclaim and a financial windfall and were further intended to advance their political agenda".

The suit filed on Tuesday (Sept 21) comes as the former president continues to argue falsely that the 2020 election was stolen from him, and as his family company, the Trump Organisation, and its longtime chief financial officer Allen H. Weisselberg have been accused by Manhattan prosecutors of avoiding taxes on employee perks that should have been reported as income.

They have pleaded not guilty.

During his 2016 presidential campaign, Mr Trump promised to make his tax returns public, as presidential candidates, including President Joe Biden, have done for at least 40 years.

But Mr Trump then refused to release them, citing an ongoing audit. The secrecy surrounding his taxes led to criticism and questions that dogged him throughout his presidency.

The documents that Ms Mary Trump provided were the basis of a 2018 article that delved into what the Times called Mr Donald Trump's history of tax dodging and outright fraud, according to the lawsuit.

The Times report cast doubt on Mr Trump's claim that he was a self-made billionaire who rose to wealth and fame with little help from his father, a real estate developer.

Instead, the investigation found, Mr Trump inherited the equivalent of at least US$413 million (S$558 million), much of it through "dubious tax schemes".

The Times reported that Mr Trump and his siblings set up a sham corporation to disguise millions of dollars in gifts from their parents, and that Mr Trump helped his father take improper tax deductions worth millions more.

In 2019, three Times reporters - Mr David Barstow, Ms Susanne Craig and Mr Russ Buettner - were awarded a Pulitzer Prize for explanatory reporting for that article and others about Mr Trump's taxes.

In announcing the award, the Pulitzer judges called the work "an exhaustive 18-month investigation" that "revealed a business empire riddled with tax dodges".

In a statement on Tuesday evening, the Times defended the news organisation's reporting on Mr Trump's taxes and said it planned to fight the lawsuit.

"The Times's coverage of Donald Trump's taxes helped inform the public through meticulous reporting on a subject of overriding public interest," the statement read. "This lawsuit is an attempt to silence independent news organisations and we plan to vigorously defend against it."

Mr Trump's lawsuit also asserts that Ms Mary Trump described her "unauthorised disclosure of the confidential records to The Times" in a book she published last year, Too Much And Never Enough: How My Family Created The World's Most Dangerous Man.

The suit says that she also made statements in the news media after the book's publication, "displaying her blatant and wanton disregard for her confidentiality obligations under the settlement agreement".

According to the lawsuit, the litigation stemming from Mr Fred Trump's will and a lawsuit brought by several family members, including Ms Mary Trump, was settled in 2001 on terms that included "confidentiality and nondisclosure obligations" binding on the parties. Ms Mary Trump could not immediately be reached for comment on the lawsuit.

Mr Donald Trump ultimately lost a bitter and protracted legal battle that twice reached the US Supreme Court, which resulted in Manhattan prosecutors' obtaining reams of tax and other financial records from his accountants.

Taxes are also at the centre of an ongoing criminal case against Mr Trump's family business and against Mr Weisselberg, who is accused of avoiding taxes on about US$1.7 million in company perks.

A trial is scheduled to begin next summer. Prosecutors from the Manhattan District Attorney's Office, which has spent years investigating the case, have not accused Mr Trump of wrongdoing.