Lindsay Lohan VIOLATES REHAB DEAL !!!

Lindsay Lohan is in BIG TROUBLE ... She's thumbing her nose at prosecutors and flying to California tonight ... presumably to enter a rehab facility that is not part of her plea deal.

Sources familiar with the situation tell TMZ ... Lindsay is about to board a private jet in NYC. 

TMZ broke the story ... Lindsay's lawyer and prosecutors agreed she would enter the Seafield Center rehab facility in Westhampton Beach, New York.  She's required to show up by tomorrow morning.

But as we reported earlier, Lindsay was freaked out because Seafield won't allow her to smoke.  We're told she may be headed for Morningside Recovery in Newport Beach, CA ... which does allow smoking.

Problem is .... prosecutors did NOT sign off on Morningside.  What's more ... we've learned NO ONE from Lindsay's camp has contacted either the L.A. City Attorney or the Santa Monica City Attorney to get the change of plans approved.

In short ... by not entering Seafield ... Lindsay has violated her plea deal.  Lindsay's lawyers are in court tomorrow along with prosecutors, where her attorneys are required to show proof of enrollment in Seafield.  It's a good bet the judge is going to be pissed, and a better bet prosecutors will be pissed.

If the judge believes Lindsay has violated the deal, he can throw her in jail for 90 days.