The GMB has stepped up its campaign to end the beer tie by releasing figures today revealing the disparity between the price of a pint across the UK.
The survey, to be released at the TUC Congress, shows that pubcos are charging an average of between £2.16 and £3.06 for a pint of lager.
The GMB claims this is between 7p and 80p above the average price of a pint at a freehouse. However the union gives the example of a freehouse as JD Wetherspoon - a managed operator, notorious for its cheap prices.
But the survey does show that in most area independent freehouses are charging less for a pint of lager than the major pubcos.
In London, for example, the average price charged by an independent freehouse for a pint is £2.54 compared to the average for an Enterprise Inns pub in the capital (£2.85) and Punch Taverns (£2.81).
The survey shows that the price of a pint of standard in the UK ranges between £1.68 and £3.53, with the average being £2.50.
Samuel Smith pubs in Yorkshire are selling the cheapest pint of lager in the UK at an average of £1.68, according to the survey. All the Tadcaster brewer's pubs are managed, selling only its own products.
London has the highest average price of a pint of standard lager at £2.72, while the North East is the lowest with the average being £2.26.
Martin Smith, GMB national organiser said: "The TUC Congress will be told that this GMB analysis shows that the big pubcos, which dominate the pub industry in the UK, are charging an average of between £2.16 and £3.06 for a pint of standard lager.
"This is between 7p and 80p a pint above the price at a free house such as Wetherspoons, depending on the UK region."
He added: "The big pubcos have tied their pub tenants to buy wholesale from them at up to 80p per pint more than the price in the wholesale market. This is translating into higher retail prices for the customers and into poor living standards for the tenants."
The survey, carried out by CGA Strategy, will also be used in the GMB's submission to the Office of Fair Trading in relation to CAMRA's super-complaint and as part of a bid to ensure the beer tie is covered by European competition rules.