Current law only requires a referendum if Israel gives up east Jerusalem or the Golan Heights, war-won lands it annexed.
It's unclear if adding the West Bank would make it harder for a deal to get approved or if Netanyahu wants a wider political cover for negotiations.
Hard-liners are pushing for an amended referendum as peace talks appear possible for the first time in five years.
An official in Netanyahu's office said Wednesday that the prime minister asked for an amended referendum bill to include the West Bank.
The official spoke on condition of anonymity because he isn't authorized to talk to the media.