European Union regulators have until November to decide whether to approve Google Inc.'s $3.1 billion takeover bid of online advertising group DoubleClick. Meanwhile, Microsoft Corp. has launched a behind-the-scenes opposition campaign against the deal.

Public relations firm Burson-Marsteller, which Microsoft retains, has warned more than 100 companies and organisations that the deal would further strengthen Google's already tight hold in online advertising, the Wall Street Journal reported Monday.

If EU regulators are unable to make a decision by Oct. 26, they could opt to investigate the matter further to decide if any changes need to be made to the deal to rule out possible antitrust concerns. The more in-depth investigation could take up to four months, the Associated Press reported.

And not only Microsoft is complaining about the deal. Yahoo Inc. and data privacy advocates also say the merger would give Google too much control over Internet advertising and personal information, according to the AP. Consumer advocacy groups in Europe and the United States are asking regulators to decide whether Google would have too much information on what people all over the world search for – valuable information to the online advertisers the company sells to.

DoubleClick, based in New York, helps marketers buy and track online advertising, including search ads, and places ads on Web sites targeted consumers are likely to use, which means more ad revenue for publishers and pages with less traffic.

The Wall Street Journal stated in an article it has seen Burson-Marsteller's pitches, which have been made in recent months. According to the report, Burson-Marsteller states the deal belongs in part of a larger discusson on “fair and free competition” in online search and privacy rights.