The US president was speaking after a Washington DC court ordered the White House to return CNN reporter Jim Acosta’s press pass after it was revoked by the US Secret Service.
Mr Acosta’s press pass was taken after he clashed with the president during a news conference earlier this month.
Mr Trump played down the ruling, saying it wasn’t “a big deal”.
But, he said, “people have to behave”, adding his staff were “writing up rules and regulations” for the press to abide by, including sticking to the agreed number of questions.
“If they don’t listen to the rules and regulations we’ll end up back in court and will win,” Mr Trump said. “But more importantly, we’ll just leave, and then you won’t be very happy.”