BRUSSELS (Bloomberg) Google Inc. is being probed by European Union anti-trust regulators for allegedly discriminating against competing services in its search results and for stopping some websites accepting rival ads.

The European Commission said it’s investigating whether Google’s AdSense contracts prevent publishers from striking deals to place ads from other services on their sites. It will also look at allegations that Google limits advertisers’ ability to move data such as key search terms from AdWords to another service.

Google rivals including Microsoft Corp.’s Ciao from Bing filed an antitrust complaint against Google this year. There has been separate criticism from French, German and UK data protection regulators over Google’s Street View service that collects data from private homes.

“Given the dominance of Google in the European search market this doesn’t come a huge surprise,” said Sam Hart, a media analyst at Charles Stanley in London. Competition remedies “often end up being relatively insignificant in terms of market position” and are more likely to include “minor tweaking” of some of Google’s search functionality if they are demanded, he added.

Anti-trust regulators have power to impose fines of up to 10 percent of revenue for monopoly abuses. The EU’s highest ever penalty of 1.06 billion euros ($1.38 billion) was against Intel Corp. last year.

Google, owner of the world’s biggest search engine, said in an e-mailed statement it “worked hard to do the right thing by our users and our industry” by marking ads clearly and enabling users and advertisers to move data to other services.

Google shares fell $18.66, or 3.2 percent, to $563.45 in Nasdaq Stock Market trading at 9.56am New York time.

“There’s always going to be room for improvement and so we’ll be working with the commission to address any concerns,” Mountain View, California-based Google said. Advertising accounted for almost 97 percent of its revenue last year, or about $22.9 billion.

Joaquin Almunia, the European Union’s anti-trust commissioner, told European lawmakers yesterday that the company had cooperated with the probe “a lot”.

Google said in a separate statement that its contracts “can’t prevent users from choosing other search providers”. It said online contracts for AdSense “have never been exclusive” and that it stopped using exclusive terms for non-online contracts almost two years ago.

Advertisers can export their ad campaigns to other platforms, Google said. Ad agencies are restricted from using an AdWords tool to automatically copy data from one screen or tab to another, it said.

The commission said it will also investigate whether Google abused its dominant position by promoting its own services over rival price-comparison sites.

“This initiation of proceedings does not imply that the commission has proof of any infringements,” the commission said. “It only signifies that the commission will conduct an in-depth investigation of the case as a matter of priority.” The regulator can close probes if it finds no evidence to back up the allegations.

Jesse Verstraete, a spokesman for Microsoft, declined to immediately comment.

Google is “stifling innovation”, price-comparison site Foundem, one of the complainants, said in an e-mail. It “should not be allowed to discriminate in favour of its own services” and should clearly label its own services in search results, the UK shopping-search site said.

“Google is being very conciliatory in their initial response,” Ian Brown, a researcher at the UK’s Oxford Internet Institute, said by phone.

“Clearly any company that has the market share Google does in Europe is going to have to be very careful.”

Google has reached a series of accords with European governments and cultural groups this year, aiming to cool tensions. Last week YouTube announced an agreement with three French artistic collection agencies over compensation for online video consumption, following a similar deal with the country’s largest music-industry group.

Microsoft, the world’s largest software company, last year ended more than a decade of antitrust disputes with the EU by pledging to offer consumers an automatic choice between its own Internet Explorer and competitors’ browsers.

Yesterday’s probe announcement “represents growing concern over Google’s power and dominance, which echoes earlier antitrust investigations against its rival Microsoft”, said Greg Sterling, an analyst at Sterling Market Intelligence in San Francisco.

On September 25, the regulator said it had closed investigations into Apple Inc.’s practices after Apple relaxed restrictions on the development tools for iPhone applications and introduced cross-border iPhone warranty repair services within the EU region.