President Trump says he's revoking Secret Service protection for Joe Biden's adult children Hunter and Ashley ... despite extending the same benefits to his own offspring after his first term.

Here's the deal ... Biden assigned Secret Service security details to Hunter and Ashley shortly before leaving office in January, providing them protection until July.

Trump says he's pulling the plug early, though ... announcing Monday on social media, "Hunter Biden has had Secret Service protection for an extended period of time, all paid for by the United States Taxpayer. There are as many as 18 people on this Detail, which is ridiculous!"

POTUS says Hunter has the detail with him on vacation in South Africa and adds ... "Please be advised that, effective immediately, Hunter Biden will no longer receive Secret Service protection."

Trump also claims Ashley has 13 Secret Service agents assigned to protect her ... but he's ending the benefit.

Worth noting ... Trump gave his kids six months of Secret Service protection back in 2021 when he left office the first time ... and Biden had no issue with it. 🤷🏽‍♂️