A pub tenants union has called for Government action over the practice of "under-filling" pints of beer, which it said had become widespread in the industry.
The GMB wrote to Consumer Affairs Minister Ed Davey saying that commercial and other contracts were now based on targets which were impossible to meet without under-filling in pubs.
The union claimed there was confusion over the size of foam head on a pint of beer, with a legal minimum of 95% liquid being interpreted as a maximum by many pub chains.
The practice was making life difficult for tenants, whose rents and bonus payments were being fixed on yields that could not be achieved if pints were filled to 100% of liquid, said the union.
Officials urged the Government to order an urgent review of how the law on what constitutes a pint was being applied in pubs.
"We need this as GMB members who run pubs are being put under financial pressures to under-fill. There is a need for clarity so that when a customer orders a pint and pays for a pint, they should get a pint," said the letter.