The commission's two Republican members raised a number of questions about the proposal, including whether it would leave too much spectrum unsold for unlicensed uses. The proposal would create a nationwide swath of unlicensed spectrum.

In addition, the proposal's cap on the amount of spectrum that one carrier can buy could result in the auction not raising the US$7 billion the U.S. Congress has targeted for a nationwide public safety network, said Republican Commissioner Robert McDowell.

McDowell urged the commission to be open to alternative ideas. "This being literally, as I've said before, the most complex spectrum auction in world history, I think we should keep all our options open," he said.

Genachowski and other commission Democrats defended the unlicensed spectrum plans. WiFi, television remote control devices and garage door openers all use unlicensed spectrum, said Commissioner Jessica Rosenworcel. "Good spectrum policy" has room both licensed and unlicensed spectrum, she said.

"This is a time to be embracing and extending WiFi-like uses of spectrum," Genachowski said. "Unlicensed spectrum has a powerful record of driving innovation, driving investment and economic growth."