The "Bar Rescue" star says Vic Caroleo's been passing himself off as Jon Taffer in and around Naples, FL for more than 3 years -- and even brags openly all over social media about their resemblance.

He even boldly commented on one of Jon's posts about his new book, writing "My Twin ... so they say."

According to the docs, obtained by TMZ, Caroleo's primary gig is as a television preacher ... and in parts of NY, his sermons air just a few hours after "Bar Rescue" on the same channel. Taffer says that's no coincidence, accusing Caroleo of trying to bolster his ruse ... that HE is actually Taffer.

Jon says Caroleo has even gotten credit cards with the name "Jon Taffer" ... and he allegedly used one of them during a dinner date in Naples back in January -- a move the woman he was out with found fishy enough to rat him out.

In the docs, filed by Jon's attorneys Bradford Cohen and Michael McMullen, they say the woman contacted Taffer's office, texting that "Caroleo, while acting as Mr. Taffer, 'was extremely touchy and inappropriate.'"

And, there was another similar incident ... when a different, anonymous, woman claimed she'd been sexually assaulted by Taffer in Naples. Jon says he was actually filming in San Diego at that time, but the woman lawyered up and sent a letter describing the alleged sexual assault -- claiming the guy reached under her skirt, and also tried to force her to perform oral sex on him.

These 2 very serious allegations were apparently the final straws for Taffer, whose lawyers Bradford M. Cohen and Michael J. McMullen say, "It has become all too common now for Mr. Taffer to be blamed for or associated with various acts committed by Caroleo as he continues to impersonate Mr. Taffer in Florida, unchecked."

Taffer also claims Caroleo's freeloading off his name ... attempting to secure free products and discounted services in various establishments.