WASHINGTON, June 10 -- The anonymous phone, the kind a journalist hands a source or a woman fleeing an abuser buys with cash, may soon be impossible to obtain in the United States. A proposal moving quietly through the Federal Communications Commission would make it effectively illegal to activate a phone line without handing over a government ID, ending the so-called burner phone that reporters, domestic-violence survivors and whistleblowers have long relied on. The agency voted unanimously in the spring to advance the rule, which a recent investigation laid out in detail this week, and the public has until late June to object before it can be finalised.

Under the proposal, telecom companies would be legally required to collect a custom...