Season 3 Edit
Tony was formerly an employee at the Stamford branch and was transferred to Scranton. Tony told Michael that he found Toby Flenderson to be a very helpful guy but he didn't feel comfortable with Michael's management style which lead for him to quit. But Michael insisted that Dunder Mifflin doesn't employ quitters, and instead fired Tony. As a result of this, the company was forced to pay him severance.
Season 5 Edit
He was mentioned by Michael in the episode 17 of Season 5. Michael wanted to put a closure on their relationship as he was mean to him. But in his way back to Scranton with Pam, Michael calls him 'fat' all over again.