Updated at 1:40 p.m. on 8/15/11

A legal beef between the nation’s two largest hot dog makers is under way in federal court in Chicago, where a judge will determine whether Oscar Mayer or Ball Park franks broke false-advertising laws in their efforts to become top dog. 

At issue?  Which Chicago-based brand can say it makes the country’s greatest hot dog.

Judge Morton Denlow said “let the weiner wars begin” as he invited lawyers to begin opening remarks Monday.

West suburban-based Sara Lee is suing north suburban-based Kraft over claims made on its hot dog packaging and ads. Kraft owns Oscar Mayer while Sara Lee runs Ball Park.

Sara Lee argued a Kraft ad campaign falsely claimed it won a national taste test, when there were alleged flaws in the way those tests were conducted. An attorney for Sara Lee said taste testers weren’t given the option to put condiments on the hot dogs. When he suggested consumer should’ve been allowed to put on ketchup, the judge jokingly said that’s an area of great dispute.

Sara Lee’s attorney also focused on Oscar Mayer’s claims that it has a brand of hot dogs that are 100% pure beef. Sara Lee argues those dogs also contain other ingredients, like water and spices, and therefore aren’t 100% pure. Kraft contends the beef is pure; there’s no mystery meat. The lawsuit dates back to 2009.

Erin Lash, an analyst for Morningstar who follows both companies, said there’s good reason the brands find it worth suing each other over ads: the sales.

“We’re dealing with a very competitive space and retail meats, in particular, can be a category where consumers tend to consider price rather than brand when making purchase decisions,” Lash said.

In court filings, neither company disclosed a specific dollar amount lost because of the others’ ads. 

But the food-industry giants underscored how high the stakes are by filing thousands of pages of legal documents over three years of litigation. Judge Denlow also joked with attorneys that the court filings were longer than “Anna Karenina.”

The case could clarify how far companies nationwide can go when boasting that their product is better than a competitor.

Judge Denlow will determine the verdict, rather than a jury.