An influential privacy watchdog has asked the US government to investigate Google+, the search giant's social network, claiming it may violate people's privacy and raises anti-trust concerns.

In a letter to the Federal Trade Commission, the Electronic Privacy Information Center (Epic) says it is concerned about the changes Google has made to its service since the launch of Google+.

Google has been fighting to catch up with Facebook in the social media space in recent years. But Epic is concerned by a new feature, called "Search Plus Your World", that blends information such as comments and photos posted on its Google+ social network into users' search results.

The service will also display Google+ business pages and notable Google+ users alongside the search results. The service aims to give users search results that are customized to their interests and connections. But Epic is concerned that it may make people's private information searchable without their knowledge and that the changes potentially favour Google's own services over those of rivals.

"Incorporating results from Google+ into ordinary search results allows Google to promote its own social network by leveraging its dominance in the search engine market," Epic writes in the letter.

The move has already been criticised by rivals, including Twitter, and by independent analysts.

In a statement released to the Guardian, a Google spokesperson wrote:



Our goal with search has always been to provide the most relevant results possible. That's why for years we've been working on social search features to help you find the most relevant information from your social connections no matter what site it's on. Search plus Your World doesn't change who has access to content, it simply helps people rediscover information they already have access to. We've taken special care with our new features to provide robust security protections, transparency and control for our users.

But Benjamin Edelman, professor at Harvard Business School, found more than a dozen Google services receiving favored placement in Google search results. "Some have developed into solid products with loyal users. Others are far weaker. But each enjoys a level of favored placement in Google search results that other services can only dream of," he wrote in a blog post.

"Google's tying tactics should not be permitted. Google's dominant position in search requires that the company hold itself to a higher level of conduct, including avoiding tying its other products to its dominant search service. Google has repeatedly crossed the line, and antitrust enforcement action is required to put a stop to these practices," wrote Edelman.

"The starting point for this is just an acknowledgement of what a valuable service Google search is. It is the dominant search engine in the world," said Marc Rotenberg, Epic's executive director. "Significant changes are likely to be looked at closely."

Rotenberg said he expects that regulators in Europe and Asia are also likely to take a close look at the changes. The European Commission is currently investigating Google for potential antitrust violations.

Last year Epic successfully appealed to the Federal Trade Commission over Google Buzz, the search giants last ill-fated venture into social media. The launch of Buzz was marred by controversy after users private details were published online.

Last March Google settled the investigation and pledged, among other things, to have independent privacy audits every two years for the next 20 years.

"The interesting thing is we thought we had that settlement here. We did push to have a comprehensive privacy programme for Google after the fiasco that was Buzz," said Rotenberg. "Google agreed and tried to say that this wouldn;'t happen again. We are asking the question at this point, has this happened again?"