The Campaign for Real Ale (Camra) presented new evidence to MPs showing that a "shocking" number of licensees who buy their supplies from so-called pubcos were on a salary of less than £10,000 a year with just one per cent on at least £45,000.
A survey of 600 publicans for Camra showed that 60 per cent earned less than £10,000 and were "substantially" worse off than those free to buy beer from any supplier.
Dave Tyler, chairman of the Telford and East Shropshire branch of Camra, said: "Certainly the pub I drink in is tied to one of the big boys and they struggle to make a living.
"Of course it's not bad for everyone, some tied pubs can make a fantastic living, but it's difficult in a county like ours where there are lots of rural and backstreet pubs.
"Those free of tie do seem to be the most successful in my opinion. My advice to anyone who wants to go into the pub business with a pub company is do your research first."
The study was published ahead of a rally in Parliament calling for curbs on big pub companies charging above-market rents and inflated beer prices.
Peter Giles, who runs the Plough Inn free-house in Shifnal after running the tied Wheatsheaf nearby, said: "You're lucky if you even make minimum wage. People are going into bankruptcy."
However, Thomas Dunn, manager of the Coalbrookdale Inn which is owned by a semi-independant pub company, said they have no extra problems due to their tie.
He said: "Obviously there are ups and downs, but it's generally good. Really you would get that with any pub. If you work together, you can make a great success."
Mike Benner, Camra's chief executive, said: "These new figures reveal the shocking truth that many licensees tied to the big pub companies are struggling to survive due to unfair business deals verging on outright exploitation.
"Pubs that are invaluable community assets are being put at risk by pub companies forcing the majority of their licensees to survive on less than the minimum wage," he added.
"The Government must push forward plans for an independent adjudicator and code of practice without delay."