As pressure mounts on Google in both Europe and the US over antitrust allegations, another European startup has thrown its hat into the ring this week. Shopping search service Twenga is to complain to the European Commission over claims that it is treated unfairly in Google search results.

As Twenga CEO Bastien Duclaux explained to The Next Web today, the company’s ranking in search results have been adversely affected by anti-spam tweaks, codenamed Panda, made by Google in recent months. Additionally, the search giant’s prioritization of its own shopping search service over rivals is “unfair and anti-competitive,” Duclaux says.

Twenga isn’t the first European company to file a complaint with European Union competition authorities over Google’s practices. Last year, the Commission began an antitrust investigation after a number of specialist, ‘vertical’ search engines complained that they were being unfairly ranked in relation to Google’s own services. In December last year, a group of German news publishers and an online maps service added their voices to the investigation. It was reported in August this year that a total of nine European companies had registered complaints.

Twenga is based in France and active in 15 countries around the world, claiming to serve over one million users with over 420,000 products from around 235,000 shops. However, in search results, Google will often place its own Google Shopping results ahead of any competitor.

Screen Shot 2011 11 04 at 13.02.41 Google threatens innovation, says French startup complaining to EU

This, in addition to an overall reduction in ranking supposedly caused by Panda updates, forced the company to reduce its expectations for revenue growth and lay off 43 of its 130 staff this summer. However, Duclaux adds that following this action, Twenga is now “in great shape” and planning to expand its product offering.

It’s not just his own company’s fortunes that concern Duclaux though. “Google is demoting competitors in every vertical they operate in. Google Places is hurting Yelp, Google Flight Search is affecting Kayak,” he states. “If regulators do not act quickly, we will have situation where Google will be dominant in every vertical. These practices threaten innovation.”

Google becoming like Microsoft?

Duclaux goes as far as to liken Google’s practices to those of Microsoft, when its bundling of Internet Explorer with Windows was seen to threaten competitors in the browser market. This eventually led to European authorities forcing Microsoft to allow Windows customers in the EU to be able to choose from a number of different browsers when they first used a new installation of the operating system.

Duclaux says he would like to see a similar ruling placed on Google, allowing users to choose from a variety of vertical search providers to appear as a high priority in their results. For example, users could opt to select Kayak for their flight search result in Google, or Yelp instead of Google Places.

That’s a solution Google’s unlikely to be happy to accept. It has always maintained that “The competition is always just a click away,” but when Google is both the main way people find services on the Web, and a provider of those services, it’s easy to see why smaller players feel aggrieved.

Twenga will submit its complain to the European Commission this month. We have approached Google for comment and will update this article if we receive a reply.