Eric Trump, the former president’s second son and a senior executive at the Trump Organization, was interviewed under oath by Ms James’s office in late 2020 following a judge’s order.
Mr Trump senior’s three eldest children – Donald Jr, Ivanka and Eric – have long been deeply involved in their father’s work.
The former president turned the business over to Donald Jr, Eric and the Trump Organization’s chief financial officer Allen Weisselberg when he took office in 2017. Ivanka moved to Washington DC to serve as a senior adviser to her father during his four-year term.
Last year, Mr Weisselberg and the Trump Organization were charged in a separate criminal inquiry into what prosecutors called a “sweeping and audacious” tax fraud scheme.
Mr Trump has said the criminal case and civil investigation into his company is a politically motivated “witch hunt”. Mr Weisselberg has pleaded not guilty.
The subpoenas for Donald Jr and Ivanka reflect an escalation in the long running legal woes facing the Trump Organization.
Ms James’ civil probe into whether the Trump Organization fraudulently inflated the values of its real estate holdings has focused on properties including the Seven Springs Estate in suburban Westchester County, New York, and the Trump International Hotel and Tower in Chicago.
The criminal investigation has been taken over by Alvin Bragg, another Democrat, who was sworn in as Manhattan’s district attorney on Saturday.
Mr Bragg told CNN last month that he plans to be personally involved in the case, and wanted the top lawyers from his office to stay on.
Lawyers for the company and the Trumps were not immediately available for comment.
Meanwhile, Donald Trump endorsed Hungary’s right-wing populist Prime Minister, Viktor Orban, on Monday offering his “complete support” to the controversial leader in an unusual intervention in a foreign election.