"All citizens, called upon to participate in these proceedings, whether as a juror, a witness, or in some other capacity, must now concern themselves not only with their own personal safety, but with the safety and the potential for personal attacks upon their loved ones.
"That reality cannot be overstated," Juan Merchan said in the expanded gag order on Monday.
New York prosecutors have argued that Trump was trying to scare potential witnesses and urged Merchan to make clear that his existing gag order, which bars Trump from publicly commenting about witnesses and court staff, also applies to family members.
They were responding to a March 28 social media post by Trump, who called Merchan's daughter a "Rabid Trump Hater" in a social media post and called for the judge to be removed from the case.
"Family members of trial participants must be strictly off-limits," prosecutor Matthew Colangelo wrote. "Defendant's insistence to the contrary bespeaks a dangerous sense of entitlement to instigate fear and even physical harm to the loved ones of those he sees in the courtroom."
Merchan's daughter runs a digital marketing agency called Authentic Campaigns, which works with Democratic candidates and non-profits.
Trump's lawyers have argued that her work poses a conflict of interest and have unsuccessfully sought to oust Merchan from the case.
Susan Necheles, a lawyer for Trump in the hush money case, declined to comment on Merchan’s expanded gag order.
Trump's defence lawyers have said Trump's posts did not violate the gag order and were not meant to interfere with the proceedings or cause any harm.
"President Trump must be permitted to speak on these issues in a manner that is consistent with his position as the leading presidential candidate," his lawyer Todd Blanche wrote.
Trump is set to go on trial starting April 15 in New York state court in Manhattan on criminal charges of covering up a $US130,000 ($NZ218,000) payment before the 2016 election to porn star Stormy Daniels to buy her silence about an alleged sexual encounter.
Trump has pleaded not guilty to 34 counts of falsifying business records and denies an encounter with Daniels, whose real name is Stephanie Clifford.
Trump could face fines or jail time if he violates Merchan's gag order, which does not bar him from criticising the judge or Manhattan District Attorney Alvin Bragg, whose office brought the charges last year.
The case is one of four criminal indictments Trump faces as he prepares to challenge Biden in the November 5 election. He has pleaded not guilty in the other three cases, which stem from efforts to overturn his 2020 loss to Biden and his handling of sensitive government documents after leaving office in 2021.
Trump faces a similar gag order in his Washington, D.C. criminal case over his efforts to reverse the 2020 election results.
