The GMB union is encouraging licensees to take industrial action against the pubcos before Christmas - but trade leaders have warned publicans to tread carefully.
Last week the union said it sent letters to 37,000 pubs in the UK and held a number of roadshows as part of its campaign against the pubcos.
It is urging tenants and lessees to become members and to take industrial action to secure "substantial cuts in wholesale prices" and to resolve "a wide range of grievances".
GMB national officer Paul Maloney said the union is planning to ballot licensee members in the next 10 days on whether to take action.
"This is a trade dispute which is why we are involved. We would like to do the ballot and action before Christmas," he said.
In response to suggestions that pubcos could evict licensees for breach of contract, he said: "If they want to throw 20,000 people out of their pubs let them play it that way because this is more than an issue affecting pubs, it is about communities.
"It would be very unwise on their part to take that action - they will be blocking up the court system."
But employment lawyer Jennifer Maxwell-Harris, of Joelson Wilson, warned licensees "they could be in breach of their contractual terms" with pub companies.
She said: "Where they (the GMB) might not be advising correctly is where people are self-employed rather than having employee status and as result there is unlikely to be any collective agreement in place between the union and an employer."
Trade leaders have also warned tenants and lessees of the risks of taking action that could involve withdrawing payments for rent and beer.
Neil Robertson, chief executive of the BII, said: "Our advice to members is to think very carefully before doing what we believe is breaking the law.
"As a professional body we would say don't do it because you are breaching your contract."
Meanwhile, the Federation of Licensed Victuallers Associations is encouraging members who are considering taking action to seek legal advice.
And Bill Sharp, licensee of the King's Arms, Bankside, London, who represented the Guild of Master Victuallers at the recent mediation talks, said the trade group would not recommend the action.
"The same rules that apply to people who are employed do not apply to people who are self-employed.
"It might give pubcos the inconvenience they deserve but it does seem strange for the GMB to be recruiting in an area where people are self-employed."
Any industrial action would follow hot on the heels of a protest at Parliament on Monday by Justice for Licensees, urging MPs to support the findings of the Business and Enterprise Committee report, which was highly critical of pubcos.