The carrier on Monday confirmed to CNET that when customers now buy handsets from Verizon, they’ll be locked until a customer signs up for service and activates them on the network. Sometime later this year, Verizon plans to keep the phones locked for an unspecified amount of time after activation and then will unlock them when that period is up.

According to Verizon, the move will help to address what it says is troubling smartphone theft. The company says that people are entering its stores and buying unlocked phones that can be used on any carrier network and quickly reselling them on the black market for a profit. By locking the phones until activation, those resellers will need to actually activate service on its network before selling the handsets. Increasing the waiting period to unlock the smartphone to after activation could further reduce theft, Verizon argues.

Get Data Sheet, Fortune’s technology newsletter

Although Verizon’s competitors have similar phone-locking features in place, Big Red signed a deal with the U.S. Federal Communications Commission (FCC) more than a decade ago in which it promised to sell all of its phones unlocked. In return, Verizon was allowed to acquire 700MHz spectrum that now powers its 4G LTE network.

In a statement, a Verizon spokeswoman told CNET that the “change does not impact the spirit of that agreement” because it’s a move to thwart smartphone theft. The company added that armed robberies at its locations were up more than 200% last year compared to 2016. Those robbers could then take the phones they’ve stolen and sell them on the black market, netting a hefty profit. Their customers would have unlocked handsets that they could bring to any carrier store and use it as their own.

Verizon has begun its policy shift now. The company will extend its unlocking timeline sometime this Spring, and plans to provide more details on the move at that time.