Two Sonoma County residents are accusing Anheuser-Busch of watering down its beer.

John Elbert and Nina Giampaoli claim Budweiser, Michelob and other Anheuser-Busch brands have 3 to 8 percent less alcohol than advertised on the labels.

They joined plaintiffs in Pennsylvania, New Jersey and other states in filing a class-action lawsuit last week in federal court in San Francisco.

"I think it's wrong for huge corporations to lie to their loyal customers," Giampaoli said in a statement Tuesday provided by her lawyers, Joshua Boxer and Robert Miller of San Rafael. "I feel really cheated."

Anheuser-Busch InBev called the claims "groundless" and said its beers fully comply with labeling laws.

"Our beers are in full compliance with all alcohol labeling laws. We proudly adhere to the highest standards in brewing our beers, which have made them the best-selling in the U.S. and the world," Peter Kraemer, vice president of brewing and supply, said in a statement.

The suit involves 13 breweries and 10 Anheuser-Busch products: Budweiser, Bud Ice, Bud Light Platinum, Michelob, Michelob Ultra, Hurricane High Gravity Lager, King Cobra, Busch Ice, Natural Ice and Bud Light Lime.

Anheuser-Busch, based in St. Louis, Mo., merged with InBev in 2008 to form the world's largest alcohol producer, headquartered in Belgium. In 2011, the company produced 10 billion gallons of malt beverages, 3 billion of them in the U.S., and reported $22 billion in profits, the lawsuit said.

According to the lawsuit, the company has sophisticated equipment that measures the alcohol content throughout the brewing process and is accurate to within one-hundredth of a percent.

But after the merger, the company increasingly chose to dilute its popular brands of beer, the lawsuit alleged.

"Because water is cheaper than alcohol, AB adds extra water to its finished products to produce malt beverages that consistently have significantly lower alcohol content than the percentage displayed on its labels," the lawsuit stated.

Giampaoli said she bought one six-pack of Budweiser a week for the past four years. Each can claimed it contained 5 percent alcohol, but her lawyers said the amount was really 4.7 percent.

Elbert bought the company's malt beverages which were labeled 5 percent alcohol, the suit said.

They could not be reached for comment Tuesday.

The suit also named two Pennsylvania plaintiffs, Thomas and Gerald Greenberg of Ambler, who said they buy six cases of the affected Anheuser-Busch products each month.

The Associated Press contributed to this story.

You can reach Staff Writer Paul Payne at 568-5312.