Andrew and Tristan Tate are being extradited to the UK ... a move their lawyer says is totally unfair given their other legal entanglements.

Joseph McBride tells TMZ ... the two brothers were arrested and are set to be extradited to the UK after the Crown Prosecution Service announced 32 more charges against Andrew and 6 against Tristan this weekend. CPS says all the charges are connected to alleged conduct which they say occurred between 2010 and 2017.

According to CPS, Andrew's 32 charges break down to 7 counts of rape, 3 counts of arranging or facilitating trafficking for sexual exploitation, 3 counts of assault, and 19 charges "relating to indecent images of a child and extreme pornography."

As for Tristan, he's facing 1 count of sexual assault, 2 counts of rape, and 3 counts of arranging or facilitating trafficking for sexual exploitation.

This is in addition to the previously announced 21 charges -- 11 for Andrew, 10 for Tristan -- CPS handed down in May of last year.

McBride says the brothers are not supposed to be extradited in the middle of the ongoing proceedings in Romania ... and, they're also just about to go to trial in Palm Beach for a defamation case -- further complicating this arrest.

McBride claims CPS "conjured up 32 new charges" overnight or early this morning ... claiming they are "ridiculous, salacious, and meant to make headlines." He claims there's no evidence backing the allegations.

McBride adds, "What's important to know is despite all the horrible allegations against these guys, they have been traveling the world the past few years without incident. They have been making court appearances in Romania and not missing a single one. We are going to trial in Florida and it looks promising, If we win, the entire narrative collapses."

He claims this is direct interference in two American citizens' due process rights by a foreign country ... and it was only undertaken by the UK because they're out to get Andrew and Tristan.

We broke the story ... U.S. Marshals took the two brothers into custody in downtown Miami on Saturday right outside a bareknuckle boxing event Andrew was set to cohost.

Story developing ...