U.S. Federal Communications Commission Chairman Kevin Martin has expressed doubts over Google's plan to bid on wireless spectrum at an upcoming auction, according to a Bloomberg report.

Last week, Google sent an open letter to the FCC pledging to spend a minimum of $4.6 billion at the auction, if the agency agreed to require the winning bidder to operate the spectrum on a wholesale basis.

Google's competition for the spectrum includes a number of telecom companies such as AT&T and Verizon.

Martin expressed concern that Google's requirement would discourage the winning bidder from building out the network.