The tax forms were obtained by Pulitzer Prize-winning journalist David Cay Johnston, and reported on MSNBC's "The Rachel Maddow Show" on Tuesday. Johnston, who has long reported on tax issues, said he received the documents in the mail, unsolicited.
But in a tweet Wednesday, Trump asked, "Does anybody really believe that a reporter, who nobody ever heard of, "went to his mailbox" and found my tax returns? @NBCNews FAKE NEWS!"
Trump has refused to release his tax returns, saying he is under a routine IRS audit.
The returns showed that Trump paid an approximately 25% effective tax rate thanks to a tax provision he has since sought to eliminate.