T-Mobile and AT&T this week responded to the FCC’s proposed rule requiring providers unlock phones within 60 days of activation—even if they’re under contract and not paid off yet.

The carriers claim that locked phones are more affordable and less prone to fraud and theft. The FCC wants to require all mobile carriers to unlock mobile phones within 60 days of activation. But neither AT&T nor T-Mobile are on board with that idea.

T-Mobile and AT&T say US regulators should drop a plan to require unlocking of phones within 60 days of activation, claiming that locking phones to a carrier's network makes it possible to provide cheaper handsets to consumers.

T-Mobile has said that its customers could see handset subsidies reduce by as much as 70% should the FCC's new rule go into effect.