According to the Wall Street Journal, the FTC has put together a team of lawyers and may stop Google from taking over the company. The FTC is also believed to have sent letters to AdMob competitors taking depositions that could be used in a blocking move.
The proposed deal is that Google buys AdMob for $750 million but the FTC is worried that the search giant could make serious incursions into a technology area that would be new for it.
Authorities in both Europe and America are already investigating Google over other antitrust concerns.
But Google is in meetings with officials and is lobbying the FTC to allow the takeover to go ahead.
The Journal said that the FTC has also told Congress of its concerns about the acquisition. But the FTC and Google may reach an agreement before formally moving to block the deal.