Google's rivals have called for close scrutiny of its $3.1 billion purchase of the internet ad company DoubleClick, amid concerns that it could assume a "monopolistic position" in the online market.
DoubleClick is a digital marketing technology company that offers enhanced advertising facilities such as rich media, ad serving and video.
Google outbid Microsoft Corporation for the business, but will now have to wait up to one year to finalise the deal, which must be approved by US and European regulators.
Microsoft is among a host of rival on- and offline media companies that are calling for an investigation. The groups are claiming that the purchase gives Google a grip on the booming online ad market.
A statement from Brad Smith, the senior vice-president and general counsel at Microsoft Corp, said: "This acquisition raises serious competition and privacy concerns. It gives the Google/DoubleClick combination unprecedented control in the delivery of online advertising, as well as access to a huge amount of consumer information."
However, Dennis Woodside, the managing director of Google UK, Ireland and Benelux, refuted the anti-competitive claims that have been levelled at the search giant.
He said: "We are talking about a competitive market. Users have a huge choice about how they search information. There are a lot of ways an advertiser can get out to market. There's nothing stopping them going to any number of online companies."
Google is confident the deal will pass a regulatory review. The move has been welcomed by Yahoo!, which is understood to have considered making a bid for DoubleClick.
Blake Chandlee, the commercial director of Yahoo! UK and Ireland, said that it was too early to determine if the deal was anti-competitive, but felt it would encourage competitiveness in the market. "This is Google's first significant move into display advertising and time will tell. This steps up the game, and I think it's good for the market and it's good for us - competition makes everyone better," he said.
Paul Mitchinson, the UK managing director of the online marketing company DGM, said: "Google could find that it runs into conflicts of interest now that it is working directly with advertisers to place advertisements on specific websites."