The Treasury is overhauling the system so levies are pegged to a drink’s alcohol content.
Some sneaky manufacturers are already making their beer and wine weaker in a bid to get around the new rules.
But smaller craft brewers which cannot change their recipes so easily will have to put prices up, pub bosses warned.
Greg Mulholland, head of the Campaign for Pubs, said: “We are concerned that some of the big brewers seem to be messing with their alcohol strength and not changing the price.
“Punters will be paying the same amount, but it will have a lower alcohol content.
“With the cost of living crisis, people are finding it hard to go out to the pub. It is the wrong time to make these changes.”
Bars and pubs are changing the drinks they sell and switching to weaker versions to keep costs down.
Kate Nicholls, head of UK Hospitality, which represents pubs, bars and restaurants, said: “If the price of a glass of wine increases by even 30p to 50p, customers will choose differently — and this is another challenge businesses don’t need.”
The Treasury is trying to keep the cost of pub pints down by freezing alcohol duty on draught beer, making it up to 11p lower than the duty in supermarkets