Two consumer groups have asked the Federal Trade Commission to block Google’s $750 million purchase of mobile advertising company AdMob. In a joint letter to the FTC, the Center for Digital Democracy (CDD) and Consumer Watchdog alleged that the deal was anticompetitve and raised privacy concerns for consumers.

"The mobile sector is the next frontier of the digital revolution. Without vigorous competition and strong privacy guarantees this vital and growing segment of the online economy will be stifled," wrote John M. Simpson, consumer advocate at Consumer Watchdog and CDD ExecutiveDirector Jeffery A. Chester.

The two non-profit groups argued that Google’s purchase of AdMob was an attempt to “buy its way to dominance” in the mobile advertising market. The groups also claimed the deal raised what it termed "substantial" privacy concerns.

Both AdMob and Google gather data about consumers' online behavior. AdMob targets consumers using a wide range of methods, including behavioral, ethnicity, age and gender, and education. Google already provides mobile advertising and data-based analytical services through its DoubleClick subsidiary.  The merger of AdMob intoGoogle would significantly increase the amount of data that could be used to track, profile and target U.S.mobile consumers.

“Permitting the expansion of mobile advertising through the combination of these two market leaders without requiring privacy guarantees poses a serious threat to consumers,” wrote the groups. The CDD petitioned the FTC earlier this year to specifically protect consumer privacy on mobile phones, especially involving mobile advertising.

In a post made last week on Google’s public policy blog, Google Product Manager Paul Feng said the FTC had made a second request for additional information about the deal. Calling the scrutiny “one consequence of Google's success”, Feng said Google would work closely and cooperatively with the government agency.

“While this means we won't be closing right away, we're confident that the FTC will conclude that the rapidly growing mobile advertising space will remain highly competitive after this deal closes,” Feng said.

The acquisition of AdMob would allow Google to expand its efforts in mobile advertising, in-app advertising and web display ads. Google’s current focus is search ads.

Mobile advertising is still in its nascency. Television and Internet ads dominate the advertising landscape, and growth in the mobile ad segment has been sluggish. Many in the industry viewed the November announcement of Google’s planned acquisition of AdMob as a long-awaited validation of the mobile advertising platform.