The ex-Prez got slapped with some sanctions Tuesday in NYC, where a court imposed a $9,000 fine -- a thousand for each violation of the gag order that's been issued in this case, which demands everyone shut their yap and not make public statements ... including DT.

While it might seem like small potatoes -- and it certainly is for a guy like Trump -- hizzoner held the prospect of temporary incarceration over Trump's head if he kept running his mouth.

The judge reportedly said ... "While $1,000 may suffice in most instances to protect the dignity of the judicial system … it unfortunately will not achieve the desired result in those instances where the contemnor can easily afford such a fine."

He added ... "Defendant is hereby warned that the Court will not tolerate continued willful violations of its lawful orders and that if necessary and appropriate under the circumstances, it will impose an incarceratory punishment."

There's been a lot of speculation over what the prospect of Trump being jailed would logistically look like from the Secret Service side of things -- seeing how he's afforded 24/7 protection as a former POTUS.

As we reported ... the Secret Service says it's prepared to head into the pokey with DT if push comes to shove -- and while the possibility of that seemed slim, it now sounds like a very realistic outcome if Trump doesn't stay quiet -- and knowing him, he probably won't.

Most of the violations of the gag order that Trump got dinged for today come courtesy of his gripes on Truth Social -- which often get screenshot and posted on X and elsewhere. The judge has ordered the offending posts to be yanked immediately by Trump and his team.

He's called the gag order unconstitutional, and like everything else ... he's called the trial at large a witch hunt. Trump has also attacked the judge specifically ... suggesting he's corrupt.