The Federal Trade Commission Friday cleared Microsoft's plan to acquire Internet ad company aQuantive.

"The FTC has reviewed the proposed acquisition of aQuantive by Microsoft," said Tom Phillips, a spokesperson for the Seattle-based company. "We've cleared that regulatory milestone."

In keeping with its normal regulatory review process of mergers and acquisitions, the FTC's 30-day Hart-Scott-Rodino waiting period elapsed without the issuance of a "second request."

"We've very pleased that the FTC opted not to make a second request," said Phillips.

In a May 29 SEC filing, Google said that the FTC had made "a request for additional information" concerning its planned acquisition of DoubleClick, another Internet advertising company. That deal is still being reviewed.

Between 1998 and 2005, the majority of FTC investigations involving a second request for information concluded with some concession or modification of the transaction, according to the agency.

In May, Microsoft said that would acquire aQuantive for $6 billion, its largest purchase to date. The deal is widely seen as an attempt to improve Microsoft's ability to compete against Google as a provider of search advertising.

According to Internet metrics firm comScore, Google accounted for 50.7% of U.S.-based Internet searches in May, compared to 10.3% handled by Microsoft sites.

Phillips said a closing date for the deal has not yet been determined. The next step, he said, is an August 9th meeting where aQuantive shareholders will vote on Microsoft's offer.

Last month, Internet ad firm Real Media said that the Hart-Scott-Rodino waiting period expired without a request from the FTC for additional information, clearing the way for WPP Group's planned acquisition of the company.