Trump Sues Niece, Mary, And NYT Over Tax Return Story

Donald Trump is suing his niece and the New York Times for publishing deets from his tax returns -- something he says broke a confidentiality agreement she signed with him.

The former President just filed suit against the nation's paper of record as well as one Mary Trump for allegedly getting in cahoots to obtain, share and publish his personal tax info in a wide-ranging story ... which DT says is a big no-no ... considering what he claims Mary agreed to years ago.

In the docs, obtained by TMZ, Trump alleges Mary agreed to keep the financial info confidential as part of a settlement with Trump and others back in the early 2000s -- and he claims that barred her from sharing such info. He also claims she conspired with the Times to get her hands on the tax info ... claiming they were "motivated by a personal vendetta[.]"

Trump also says this ... a reporter for the Times allegedly approached Mary relentlessly in an effort to seek these documents, which he suggests they knew were off-limits, making them just as responsible as she is for disclosing them. It's a bold claim -- and one that might be difficult to prove.

The First Amendment is wide-reaching and protects publications against this exact sort of thing -- namely, that if they get their hands on material, legally, they have every right to publish.

Trump, however, is alleging the exact opposite ... that they broke the law to obtain this stuff, which he and his lawyers will now be tasked with proving in court.

Mary has since responded to word of the lawsuit, calling her uncle a "loser" and characterized this as a desperate move. NYT says writing their stories on Trump's taxes -- which they claim showed he'd been paying little to no taxes while also absorbing massive losses in his business empire -- were of public interest.