The GMB has branded the British Beer & Pub Association's (BBPA's) threat of legal action as "bullying" and a "crude attempt" to stop the union standing up for tied tenants.
In what is now a major war of words, the GMB's Paul Kenny has gone on the offensive in response to a letter from BBPA chief executive Brigid Simmonds.
The letter threatened to apply for an injunction against the union if it continued to encourage licensees to break their contract.
"This letter from BBPA to GMB is an example of bullying from property companies that have for years got away with bullying and harassing their tied tenants," said Kenny.
"BBPA have picked the wrong organization to bully. GMB will stand for the legal rights of their tenants."
The response comes as GMB members are due to meet with pubs minister John Healey in Parliament, as part of a union lobby day.
Kenny also warned that his union would continue to challenge the pubcos in court over evictions, alleged "unfair claims for debts" and alleged "misuse of pubco contract powers".
He added: "These property owners' assertion that their tied tenants do not enjoy the immunities that Parliament has given organized workers is self serving. The tied tenants are one of the most exploited groups of workers in the land."
"For BBPA to say that tied tenants may sue GMB if they lose their business is like Dick Turpin calling for more police constables given the number of tied tenants who have lost their business through the pubco model."