Thinking outside the bun to promote one of his state's chief industries, Montana Sen. Jon Tester on Monday offered to beef up Taco Bell's filling with Montana-bred cattle.

Weighing in on a class action lawsuit that claims the nation's largest Mexican cuisine fast food chain is guilty of false advertising, Tester, a first-term lawmaker, third-generation farmer and longtime butcher, said Montana's ranchers "raise the best cattle in the world."

"When I go to a restaurant, I expect the beef I order to be beef -- not 'filler' -- and my guess is most Montanans, and Americans feel the same way," said Tester, 

"If Taco Bell needs to beef up, they can give their customers the highest quality meat around by using Montana beef, and in the process, supporting agriculture jobs in Montana. And that's a win-win."

The lawsuit, filed in California last week by the Alabama law firm Beasley, Allen, Crow, Methvin, Portis & Miles, alleges that the taco filling is less than 35 percent actual beef, though the firm would not say who tested the meat or provide other details about the analysis. 

In response to the suit, Taco Bell took out an ad in nine major newspapers with a headline "Thank you for suing us."

In the ad, the company claims that the taco filling in its menu items are 88 percent beef and 12 percent "secret recipe" made up of a not-so-secret combination of water, spices and a mixture of oats, starch and other ingredients that contribute to what it calls the "quality of its product."

Gene Grabowski, chairman of the crisis and litigation practice at Levick Strategic Communications in Washington, told The Associated Press that Taco Bell must be confident of its beef filling if it's willing to take its legal dispute public.

"It is unusual for a company to take this on and challenge the allegations so boldly," said  "A lot of companies are going to be watching how this turns out."