Eric Trump - who serves as executive vice president of the Trump Organisation - gave a "false" explanation about why he failed to appear for a deposition investigating the family business, New York's attorney general said in court papers on Tuesday.
The state is probing the president's business for improperly inflating the “value of Mr Trump's assets on financial statements in order to secure loans and obtain economic and tax benefits”.
Eric, the president's third child and second son, had been called upon to give testimony in the investigation, after New York took action to enforce a raft of subpoenas. Mr Trump's lawyers said their client had adjourned the deposition to get “certain assurances first.”
But New York attorney general Letitia James dismissed that claim, saying that the assertion was "false". Mr Trump gave his “categorical refusal to appear” through a July 27 letter from his lawyer, she said.
Earlier this month, Mr Trump said in a court filling issued through his lawyers that he would be willing to comply with the subpoena - but only after November's election.
The lawyers argued Eric Trump’s “extreme travel schedule” related to his father’s reelection campaign prevented him from testifying sooner in the civil probe.
They also wanted “to avoid the use of his deposition attendance for political purposes.”
Attorney general James, a Democrat, hit back at the scheduling claims and warned Mr Trump he was not above the law.
"We won’t allow any entity or individual to dictate how our investigation will proceed or allow anyone to evade a lawful subpoena," she said in a statement. "No one is above the law, period.”
Attorney general James sought court intervention after Mr Trump's lawyers abruptly canceled an interview with investigators that had been planned for late July.
The civil investigation was launched in 2019 after the president's longtime personal lawyer Michael Cohen told Congress that he had repeatedly inflated the value of his assets to obtain more favorable terms for loans and insurance coverage.
Additional reporting by Associated Press