Mary Kay Letourneau's Husband Must Cut Back on Weed, Booze Under Terms Of Plea Deal

Mary Kay Letourneau's husband is being forced to cut back on the partying ... 'cause the plea deal in his DUI case calls for him to tone down his alcohol and cannabis consumption.

Vili Fualaau pled guilty to reckless driving and, as part of his sentence, he's getting an ignition interlock device installed in his car. If he has any booze, the car won't start.

He's also prohibited from having any liquor or recreational drugs for at least 8 hours prior to getting behind the wheel ... plus he's got to complete a substance abuse course.

Vili will also spend 5 days in a community work crew program. As long as he completes these terms and keeps his nose clean for the next 2 years, Vili won't serve any jail time.

TMZ broke the story ... Vili was busted for DUI this February in Washington and prosecutors say he had THC in his blood and a BAC of .08.

We've got some ideas for ways Vili can release stress without his vices ... after all, he's been banging Mary since he was 13.