Google expects FTC to clear AdMob deal, citing new Apple iAd service

Their claim would likely assert that Google's historic dominance of the online advertisement market affords the company an unfair advantage in the mobile phone world, especially on new devices that run on its Android operating system.

Lawmakers too are growing concerned about the AdMob buy. Among the skeptics is Sen. Herb Kohl (D-Wis.), the chairman of his chamber's subcommittee that primarily handles anti-trust issues. While the senator stressed in a letter to the FTC that he had not yet made up his mind on the proposed deal, he nonetheless called for a rigorous investigation of its effects on the mobile marketplace.

"Allowing any one firm to dominate this market could result in higher prices for mobile advertising on the Internet and with respect to smart phone applications, and also could result in lower revenues realized by applications developers," Kohl wrote in the letter.

"The importance of this transaction is heightened because of the likely importance of the smart phone advertising market in the future," he added.