The complaint by Microsoft underlines the mounting rivalry between the two companies.
Microsoft and the other companies expressed their concerns informally, the people said, declining to provide details about the nature of the complaint about Google+ or the names of the other complainants because of the sensitivity of the matter.
The European Commission declined to comment and Microsoft said it would not comment on “rumors or speculation.”
Google, the world’s most popular Internet search engine, launched Google+ last June, pitting it against Facebook, the world’s biggest social network, and Twitter, among others.
The new service allows users to play games and share photos with friends, incorporates a video chat facility and offers a more personalized search service by integrating it with the original Google engine.
Last month, the US Federal Trade Commission expanded its investigation into the company’s search activities to include Google+, a source familiar with the matter has told Reuters.
EU Competition Commissioner Joaquin Almunia reiterated on Tuesday he would decide by the end of March or early April the next step in the regulator’s ongoing investigation into Google, and charges by rivals that it misused its market position.
“We continue to receive information and complaints or informal complaints, so it’s not a simple task to investigate,” Almunia told lawmakers at the European Parliament.
The Commission launched the investigation in November 2010 after rivals, including Microsoft, accused Google of abusing its dominant position in the market for web search services. There are now 12 complaints.
Microsoft last week asked the European Commission to step into a patent dispute with Google and Motorola Mobility, accusing the US mobile phone maker of setting excessive charges for the use of its patents in Microsoft products.
EU and US regulators have given approval for Google to buy Motorola Mobility.
Motorola is also the subject of complaints by Apple , which has asked the EU regulator to take action against the mobile phone firm over patent licensing.
