Among the revelations was that Mr. Trump reduced his taxable income by deducting about $26 million in fees to unidentified consultants as a business expense on numerous projects between 2010 and 2018.

Some of those fees appear to have been paid to Ms. Trump, The Times found. On a 2017 disclosure she filed when joining the White House as a presidential adviser, she reported receiving payments from a consulting company she co-owned, totaling $747,622, that exactly matched consulting fees claimed as tax deductions by the Trump Organization for hotel projects in Hawaii and Vancouver, British Columbia.

The subpoenas were focused on fees paid to the firm on her disclosures, TTT Consulting L.L.C., and represented just a portion of the $26 million, according to a person with knowledge of the matter. The name of the firm appears to be a reference to Ms. Trump and other members of her family.