French insurer Axa is to sue Google in a dispute over trademarks which could threaten the web search firm's advertising revenues.
Google is gearing up for a stock market launch
Axa claims Google allows rivals to buy online adverts which appear when searches are made for names and phrases the insurer has trademarked.
The insurer is the latest of several firms to take action against Google for alleged "trademark hijacking".
Axa is seeking unspecified damages. A preliminary hearing is due on 10 May.
Google is facing similar lawsuits in the US from home improvements firm Wallpaper Factory and pet supplies shop Pets Warehouse.
The web search firm is also fighting a case brought in France by luxury goods firm Louis Vuitton.
Analysts said the litigation could cast a shadow over the Google's advertising business model.
"It's definitely a threat to Google, but it's also a threat to anybody who sells keyword-linked advertising," Danny Sullivan of online newsletter Search Engine Watch told the AP news agency.
Keyword-linked advertising, where firms pay to ensure that their online adverts appear whenever certain search terms are used, now accounts for about a third of all online advertising in the US.
It generates an estimated $1.6bn a year in revenues.
The latest legal challenge against Google comes as it is preparing a multibillion dollar stock market launch, one of the most eagerly anticipated market debuts of recent years.
Google is expected to argue that there is no trademark infringement as it ensures that no trademarked words or phrases appear in the text of rivals' adverts.
It claims that this prevents consumers from mistaking the advertised goods or services for those of the brand they originally searched for.