Verizon is to start locking new phones, something it calls an anti-theft measure. It’s raised some questions about whether the move breaches a deal it made with the FCC.

According to Verizon, the idea isn’t that the phone will remain locked and forcing users to take its service. At first the phone can be unlocked simply by signing up and activating service, meaning users can switch immediately. From this spring that will change and there’ll be a minimum period before unlocking is possible. Verizon says the lock will remain for a “brief period of time” but hasn’t confirmed exactly how long it will be.

Verizon says the move is to deter people from stealing phones from stores, which is a particular risk given the small size of a phone and the high price it can command among buyers who don’t ask questions about where it came from. The carrier pointed to several recent cases of armed robberies in phone stores.

Having a waiting period before allowing an unlock is hardly a rarity in the smartphone market, but it does raise some regulatory issues. Verizon won the right to operate the spectrum used for its 4G network in an FCC auction. The terms of that auction and the accompanying license specifically said Verizon could not “configure handsets it provides to prohibit use of such handsets on other providers’ networks.”

Verizon says that’s not an issue because it’s new policy does not “impact the spirit of that agreement”. It appears that were anyone to formally complain to the FCC, the onus would be on Verizon to prove that argument.