American Airlines Thursday filed a lawsuit against Google, claiming the search company is infringing on the airline's trademarks by using them as keyword triggers for paid advertisements by other companies.

By bringing the lawsuit, filed in U.S. District Court for the Northern District of Texas, Fort Worth Division, American wants to stop competitors from using those trademarks to trigger their own advertising on Google.

Neither Google nor American could be reached for comment.

"Without authorization or approval from American Airlines, Google has sold to third parties the 'right' to use the trademarks and service marks of American Airlines or words, phrases, or terms confusingly similar to those marks as 'keyword' triggers that cause paid advertisements, which Google calls 'Sponsored Links' to appear alongside the 'natural results," the lawsuit said.

When a user performs a search on Google's site for the words "American Airlines" to search for flights on American, the user may be redirected to the Web site of a competing airline, a Web site that sells American Airlines travel services or the services of other airlines, or Web sites that have nothing to do with air travel at all, according to the lawsuit.

This happens because those other companies pay Google to get links to their Web sites placed at the top of the list of sponsored links -- on the right hand side of the search results page -- when a user's search terms match certain keywords, such as American Airlines. The companies buy those keywords from Google.

But American alleges that Google doesn't have the right to sell its name to any other company and is asking the court to stop Google from selling its trademarks to other companies. It also wants Google to pay American any money it has made by selling its trademarks, and to award unspecified monetary damages to the airline.

"American Airlines does not bring this lawsuit lightly," American said in the court documents. "Indeed, American Airlines does not question that Google's search engine provides consumers with a powerful and highly useful means to search the Internet for information. That said, Google's search engine is helping third parties to mislead consumers and misappropriate American Airlines trademarks by using them as keyword triggers for paid advertisements and by using them within the text or title of paid advertisements."

While other companies have filed similar lawsuits against Google, American is perhaps the largest company to do so, according to a blog post by Eric Goldman, assistant professor and director of the High Tech Law Institute at the Santa Clara University School of Law.

"American Airlines apparently decided it was worth going to war over this issue and is prepared to pay the big bucks to litigate this case accordingly. If this lawsuit runs its course, I expect this to be a hard-fought and expensive lawsuit," Goldman wrote. "My working theory is that this was not a good lawsuit for American Airlines to bring."

Goldman questioned whether American has ever bought third-party trademarks as keywords. "I'd be surprised if American Airlines has run a completely clean shop," he said. "Finally, it's not in Google's nature to retaliate this way, but I wonder what would happen if Google decided to cut off keyword advertising for American Airlines."