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 only on a salary of less than £10,000 a year, with just 1% on at least £45,000.
A survey of 600 publicans for Camra showed that 60% earned less than £10,000 and were "substantially" worse off than those free to buy beer from any supplier.
The study was published ahead of a rally in Parliament calling for a clampdown on big pub companies charging above-market rents and inflated beer prices.
Camra chief executive Mike Benner 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. The inability of licensees to earn sufficient income means money cannot be invested back into pubs enabling them to grow as businesses.
"The big pub companies are contributing to the destruction of Britain's pubs by failing to support their licensees with competitive wholesale beer prices and rents. Every pub failure is a disaster for the individuals involved as well as for the local community built around that pub.
"In contrast, pub companies can profit from pub failures by retaining licensees' deposits, premiums and even selling the pub off to property developers."