EXCLUSIVE

Whatcha gonna do brother, when a former wrestling star (allegedly) threatens to KILL YOU!?

Well, if you're Hulk Hogan -- you call the cops ... because that's exactly what happened during an alleged incident in San Jose involving Hulk's former wrestling ally Scott Steiner.

Here's what we know ... Hulk's wife Jennifer flew into San Jose for WrestleMania on March 26th -- and claims Steiner grabbed her at baggage claim and said he plans to "kill Terry" [Hulk's real name] as soon as he lands.

Sources close to the Hogans tell us ... Jennifer didn't recognize Steiner and called Hulk immediately -- who took the next flight into S.J. and went with her to file a police report early the next morning.

We're told cops are now investigating Steiner for "felony terrorist threats" -- and so far, officials have already gathered airport surveillance video which we're told shows Steiner confronting Jennifer.

As for Steiner, he's been very public about his dislike of Hogan for years -- and blames him for the demise of WCW wrestling ... where Scott and Hulk were allies in the NWO.