The company said that when trademarked terms such as American Airlines or Aadvantage are entered into a Google search, sponsored links are listed alongside the results. These targeted ads link to rivals’ web sites and web sites for companies selling tickets for other airlines.

This lawsuit involves…efforts by certain companies to free ride on American Airlines’ brands through use of Google’s technology, said the company in its filing. It is seeking unspecified damages.

Sponsored ads based on a pay-per-click system are Google’s prime revenue generator but the company acknowledges that usage needs to be properly managed. In a statement, the company said: We are confident that our trademark policy strikes a proper balance between trademark owners’ interests and consumer choice.

American Airlines endorses aspects of the search model. A spokesperson for the company commented: When done right, search is a great tool, but we have a problem with this part of their business.

This is not the first time Google has been challenged in the courts over the legality of its sponsored advertising model. The most well known was the case brought by insurance company Geico two years ago when the result was not a clear win for either party. Although it was ruled that it was not unlawful for the Geico trademark to be used to fire off ads from rival companies, Geico was permitted to collect damages from Google for ads that contained the Geico name in the text of rivals’ ads.