The T&G said the representative had been sacked by Driving Edge, the agency employing him, after The Daily Mail printed comments he made about working conditions. An appeal has been launched.
Mick Cashman, T&G senior organiser, alleged the dismissal was the latest in a series of problems at the Middleton depot.
He said Wincanton and Driving Edge workers, both permanently employed on the site, had different pay and conditions, which created friction.
Cashman said leafleting and petitioning were being considered for the end of next week.
A Tesco spokesman said Driving Edge was responsible for the dismissal and for determining pay and conditions at the Middleton site.