Ultimate Warrior -- Stop Selling Knock-Off Merch ... Or We'll Sue

Feel the power of the Ultimate Warrior's trademark rights ... from BEYOND THE GRAVE -- the late wrestler is trying to crush all attempts to make a quick buck off his death.

T-shirts donning Warrior's name and logo popped up all over the Internet last week after he passed ... and now attorneys for Ultimate Creations (Warrior's marketing company) want the imitations scrapped from the net -- citing the wrestler's trademark.

We're told the cease and desist letter -- obtained by TMZ -- has been fired off to more than 100 merchandisers already ... threatening legal action if they don't shut down all sales immediately.

Warrior will also gorilla press slam dead relatives of any knockoff salesmen ... in Heaven.

That's what we imagine, anyway.