Britney Spears' Ex Jason Alexander Booted From Gym Where He Allegedly Stalked Woman

Britney Spears' ex-husband, Jason Alexander, needs a new gym ... because his old gym gave him the boot after he got arrested for allegedly stalking another member.

Jason was a member at Life Time in Franklin, TN but a manager at the gym tells us Jason has officially been kicked out.

We're told Jason had his membership revoked after police opened their investigation into allegations he was stalking a woman at the gym.

TMZ broke the story ... Jason was arrested for stalking last month and his alleged victim claims he followed her out to the gym's parking lot, where she says she told him to leave her alone, only for Jason to blow up her phone with tons of calls and texts.

The woman says Jason then showed up at her house, driving by a couple times the day after the alleged parking lot confrontation ... and she also says he approached her at the gym pool when she was with her kid.

As we first reported, Jason's been ordered to steer clear of his alleged victim ... he can't contact her or post about her on social media.