Wireless microphones are one of a number of consumer gadgets — including baby monitors, Wi-Fi routers, garage door openers, television remote controls and electronic car key fobs — that enjoy unlicensed access to the airwaves and which have contributed billions of dollars to the economy. The gadgets can operate without an F.C.C. license, unlike a cellphone company, which must buy a license to operate on a certain segment of the airwaves, or television broadcasters, which operate free on assigned public airwaves.

Television stations must be spaced a certain distance apart on the airwaves to avoid interfering with each other, resulting in unused slices of spectrum available between the stations, referred to as “white space.” The F.C.C. allows the gadgets to operate in those slices.

Increasingly, however, the F.C.C. is eager to reclaim any spectrum it can from television stations and others and sell it to cellphone companies. It did so several years ago when television broadcasts converted from analog to digital signals, which allowed stations to move down the spectrum and free up a rich vein of airwaves — located roughly at frequencies from 700 to 800 megahertz — for mobile phones.

Now the F.C.C. is again seeking prime spectrum for sale to wireless carriers. Under its current plan, the commission is aiming to persuade some broadcast stations to give up their airwaves or to agree to move to another spot, freeing up for auction the bands in the 600- to 700-megahertz range, where wireless mikes and other devices often operate.

“For the hundreds of millions of Americans with mobile phones, the auction will be critical to preventing dropped calls, degraded service and rising prices as demand for mobile broadband — and the wireless spectrum it requires — continues to increase exponentially,” the F.C.C. said in a statement. “Wireless microphones play an important role,” the agency added, and it “is considering how best to ensure they can continue to operate while using spectrum more efficiently.”

But when television channels are packed more tightly into a narrower band of airwaves, there is less room between them in which unlicensed devices like wireless microphones can operate.

“The more the F.C.C. auctions off, the smaller our part gets,” said Tom Ferrugia, director of government relations for the Broadway League. Theaters and sound companies that had to move their transmitters out of the 700-megahertz band recently purchased new equipment that could operate elsewhere, he said. Now they might be forced to again spend many thousands of dollars on new transmitters.