EXCLUSIVE

The Situation is on the wrong end of a massive Federal criminal investigation -- which is currently focusing on the "Jersey Shore" star's cash flow ... TMZ has learned.

Sources tell us, Mike Sorrentino and his companies -- MPS Entertainment, Situation Productions, GTL Management, and his clothing line Situation Nation -- are at the center of the investigation.

The exact nature of the crime is unclear, but we know it's a felony, and appears to be finance related. We're told subpoenas have already been issued to Sitch's business associates, asking for copies of payments issued to him, copies of canceled checks, correspondence, and more.

We reached out to Situation's rep for comment. So far, no word back.