Drinkers of Budweiser - marketed as the "King of Beers" - are taking the company to court over allegations the popular American lager is watered down to boost profits.
A lawsuit, filed in California, accuses Anheuser-Busch of violating consumer protection laws in the state and in Missouri by "falsely representing the alcohol content of the products it sells".
It demands unspecified "compensatory damages" for anyone in the United States who has bought Budweiser products in the past five years.
The legal action - said to be based on allegations made by staff and former brewery workers - was flatly rejected by the company which is also understood to be facing similar claims in other US states.
Peter Kraemer, the firm's vice president of brewing and supply, said: "The claims against Anheuser-Busch are completely false and these lawsuits are groundless.
"Our beers are in full compliance with all alcohol labelling laws.
"We proudly adhere to the highest standards in brewing our beers, which have made them the best-selling in the United States and the world," he added.
The lawsuit claims that Anheuser-Busch can produce "a significantly higher number of units of beer from the same starting batch of ingredients" by watering down its product.
"As a result, Anheuser-Busch's customers are overcharged for watered-down beer and Anheuser-Busch is unjustly enriched by the additional volume it can sell," it alleges.
Besides Budweiser, which is sold as having 5% alcohol by volume, the lawsuit further claims that Anheuser-Busch waters down nine other brands, including Bud Ice, Bud Light Platinum and Michelob.
One of those bringing the lawsuit, Nina Giampaoli, claimed: "I think it's wrong for huge corporations to lie to their loyal customers.
"I really feel cheated. No matter what the product is, people should be able to rely on the information companies put on their labels."