Drinks firm C&C Group, owner of Tennent's Lager, said it had left the Portman Group and would now focus on smaller projects instead of being part of the industry-wide lobby group.
Paul Bartlett, C&C head of corporate social responsibility, said the Portman Group had moved away from its founding principles and his firm would no longer support its agenda. He said: "We informed the Portman Group last year that we planned to resign in order to focus our resources on a strategy of investing in community projects rather than industry lobbying.
"We remain passionate about the rights of adults to enjoy alcohol responsibly and our credentials in this area over a long period of time are very strong. We support minimum unit pricing in Scotland and across the island of Ireland because, as a local company, we understand the needs of the communities in which we play a part.
"Sadly the Portman Group has moved away from its founding principles and is now dominated by large multi-national drink companies with an agenda at odds with the wider UK industry. On this basis we feel it's time to leave."
C&C Group, which also make Magners and Blackthorn Ciders, recently announced an investment of £1m in UK orchards. The decision to walk away from the Portman Group was welcomed by safer drinking campaigners Alcohol Focus Scotland, who said that it strengthened the case for minimum pricing of alcohol.
Dr Evelyn Gillan, chief executive of Alcohol Focus Scotland, said: "We welcome C&C Group's support for minimum pricing and share their concerns about the power of the multi-national drinks companies. These global producers lobby to prevent the introduction of effective alcohol policies which will improve public health in order to protect their profits. An example of this is the minimum pricing legal challenge led by the Scotch Whisky Association, which represents some of the world's biggest alcohol firms."
With C&C opting out, the Portman Group is now has nine members: AB InBev; Bacardi Brown-Forman Brands UK; Carlsberg UK; Diageo GB; Heineken UK; Molson Coors Brewing Company (UK); Pernod Ricard UK; SAB Miller and SHS Drinks.
CEO Henry Ashworth, said: "Portman Group members lead the drinks industry in promoting responsible drinking and reducing alcohol-related harm across the UK through effective self-regulation and partnership working.
"It is a shame that C&C Group has chosen to step down from this leadership role in the UK and Ireland."