Microsoft Corp-owned Ciao from Bing has also complained to European authorities about Google's standard terms and conditions.
The European Commission is considering complaints from three online companies regarding Google Inc's practices, including its search rankings, the company said on Tuesday.
The complaints from two of the companies -- UK price comparison site Foundem and French legal search engine ejustice.fr -- allege that Google's search algorithm demotes their sites in web search results because they compete with it, Google said in a post on its corporate blog.
Microsoft Corp-owned Ciao from Bing has also complained to European authorities about Google's standard terms and conditions, Google said.
Google, the world's No 1 search engine, said it will be providing feedback and additional information on the complaints and that it was confident its business is "in line with European competition law."
Microsoft was not immediately available for comment.
Google has come under increasing regulatory scrutiny as it has grown. The US justice department has challenged Google's settlement with book publishers and author groups to create an online digital archive, and the US Federal Trade Commission is seeking more information on the competitive impact of its proposed $750 million purchase of mobile advertising company AdMob.
News of the European complaints was first reported by The Daily Telegraph in its Wednesday edition.
The paper said the European Commission has written to Google to find out how its search functions work.
"Though each case raises slightly different issues, the question they ultimately pose is whether Google is doing anything to choke off competition or hurt our users and partners," Google senior competition counsel Julia Holtz said in the company's blog post. "This is not the case."
Google had 90% of the global search market compared with 7.4% for a combined Yahoo! and Microsoft's Bing, according to November data from web research firm StatCounter.
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