Tom Sandoval's back in his all-too-familiar villain role ... he's under fire from fans and castmates for interacting with a captive tiger, and PETA is schooling him on why it's bad for big cats.
The animal rights organization fired off a letter to the "Vanderpump Rules" star after footage emerged showing him inside an animal enclosure at Tiger World Thailand, where a tiger put its massive front paws on Tom's shoulders.
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In the letter, obtained by TMZ, PETA scolds Tom for the photo op ... explaining, "When popular folks like you pose with wild animals, people are moved to support pay-to-play animal experiences, for which big-cat cubs are torn away from their mothers prematurely and denied their freedom as well as anything remotely natural and important to them."
More specifically, PETA's also schooling Tom on tigers ... it says wild tigers avoid humans and are naturally solitary and reclusive, adding, "Any human interaction with big cats poses dangers for both humans and the felines, and captive big cats have attacked and killed their captors and visitors."
While Tom walked away from the visit physically unscathed ... he's taking heat online from fans and his 'VPR' cast members, Lala Kent and James Kennedy.
PETA's telling him to consult them the next time he has the urge to hit up a zoo.