The House version, sponsored by Rep. Greg Walden (R-Ore.), would prohibit the FCC from designating additional airwaves for unlicensed use. Unlicensed spectrum, which can be used by any company for free, powers technologies such as Wi-Fi, garage door openers and remote controls.
In their letter, the senators argued that Congress should allow the FCC to make its own decision about how best to use the airwaves.
"In the rush to fill the Treasury’s coffers with revenue from spectrum auctions, we must not neglect the fertile ground for innovation that unlicensed spectrum offers and the subsequent economic value it produces," the senators wrote.
"It may be that the spectrum cleared is best left for licensed use, but Congress should defer to the FCC to make the proper determination of optimizing the allocation of spectrum given the dynamic nature of the industry and wireless technologies."
But House Republicans argue the government should not pay to reclaim airwaves that it will then give away for free.
The senators also criticized the House bill for prohibiting the FCC from imposing various conditions on which companies can buy spectrum leases at auction.
"While at first this may seem appropriate to ensure an open auction where all can take part and would be in a market with perfect competition, upon closer examination this could have a deterring effect on fostering competition and maximizing auction proceeds to pay for a public safety network and deficit reduction," they wrote. "Maintaining the FCC’s current range of tools for structuring a spectrum auction, as prescribed by the statute, provides the agency with the requisite flexibility to attract a sufficient number of bidders to ensure the competitive bidding necessary to maximize auction revenues and that the market for spectrum remains competitive for companies of all sizes."
The letter emphasized that companies should find new ways to use the airwaves more efficiently.
"Spectrum alone will not solve the looming spectrum crisis, but it will require a combination of spectrum, technology and infrastructure," the senators wrote.