The head of a consumer online privacy watchdog says U.S. regulators should look into Google's new personalized search to see whether there are antitrust or privacy issues.

"Google is an entrenched player trying to fight off its challenger Facebook by using its market dominance in a separate sector," Marc Rotenberg, executive director of the Electronic Privacy InformationCenter, told The Los Angeles Times. "I think that should trouble people."

Rotenberg also said the personalized results will make personal data of users on Google+ more accessible, which may raise privacy concerns. He said he is considering filing a complaint with the Federal Trade Commission, asking the agency to investigate the Google search update.

"We believe this is something that the FTC needs to look at," he said.

Rotenberg declined to comment further to CNET on his plans, only saying "We will have news tomorrow."

An EPIC blog post on Tuesday provides more details on what the group is worried about.

"Although data from a user's Google+ contacts is not displayed publicly, Google's changes make the personal data of users more accessible. Users can opt out of seeing personalized search results, but cannot opt out of having their information found through Google search," the post says.

This wouldn't be the first complaint against Google for anti-competitive behavior.

"Recently, the Senate held a hearing on Google's use of its dominance in the search market to suppress competition, and EPIC urged the Federal Trade Commission to investigate Google's use of Youtube search rankings to give preferential treatment to its own video content over non-Google content," (PDF) EPIC said. "Google has also acknowledged that the FTC is investigating whether Google uses its dominance in the search field to inhibit competition in other areas."

Google should not take this threat from EPIC lightly. EPIC complained to the FTC about a year ago over Google Buzz, alleging Google was violating Gmail users' privacy rights by using their contacts and activities to build out the social network, which was opt-out. A month or so later, the FTC and Google announced a settlement that requires Google to undergo independent audits of its privacy practices for 20 years and to make new features opt-in if they provide additional sharing of certain types of private information. Meanwhile, Buzz was shut down in October after Google+ reached 40 million users.

Google's new personalized search, launched on Tuesday, includes comments and photos from people in their Google+ and Picasa networks. Users can opt out. Meanwhile, real-time data from Facebook and Twitter is not available to Google searchers and Google is taking some heat for adding Google+ data to results when other social networks aren't included.

Yesterday, Twitter complained that the new Google feature dubbed "Search plus Your World" would make search results less relevant for people because it doesn't include Twitter, where people often post and search for breaking news. Twitter used to have a deal for Google to index its content in real time but that agreement expired this summer. Google claims Twitter chose not to renew the deal, and that Facebook also blocks Google from fully crawling the content on its site.

Today, Twitter General Counsel Alex Macgillivray provided an example via Twitter of how Google personalized search affects the relevancy of results. A search for "@wwe" with personalized search turned on puts the World Wrestling Entertainment Twitter profile page at the bottom of the screen, below the WWE Web site and Google+ posts mentioning WWE. A similar search without personalized search enabled provided the same results, minus results on the right side of Google+ People and Pages related to @wwe.

It makes sense for Google to offer users the option of searching Google+ like this, as my colleague Stephen Shankland points out. But it would also make sense to have results for an obvious Twitter-related search appear higher up on the page.

A Google spokesman provided CNET with this comment:

As always, our goal is to provide you with the most relevant and comprehensive search results possible. That's why for years now we've been working with our social search features to help you find the most relevant information from your friends and social connections, no matter what site that content is on. However, Google does not have ready access to incorporate all the information from some sites, so it's not possible for us to surface all that content in realtime.

Since personal results may include directly-shared information such as photos and Google+ posts, we designed the features to offer transparency, choice and security for users.

Updated 2:40 p.m. PT with Google comment and 1:36 p.m. PTwith more background and details throughout, and Twitter providing search example for @wwe.