Federal Communications Commission Chairman Ajit Pai yesterday criticized Sprint, Charter, CenturyLink, and four other phone providers for not committing to adopt a new system for blocking robocalls.

Pai issued a press release and sent letters to wireless carriers and other phone providers, saying that certain companies "have not yet established concrete plans to protect their customers" using the new "SHAKEN" and "STIR" robocall-blocking protocols.

SHAKEN stands for Signature-based Handling of Asserted Information Using toKENs, while STIR stands for Secure Telephone Identity Revisited. The new industry standard isn't expected to completely eliminate robocalls, but it may make a sizable difference and is expected to be implemented by carriers starting in 2019.

"Under the SHAKEN/STIR framework, calls traveling through interconnected phone networks would be 'signed' as legitimate by originating carriers and validated by other carriers before reaching consumers," Pai's press release explained. "The framework digitally validates the handoff of phone calls passing through the complex web of networks, allowing the phone company of the consumer receiving the call to verify that a call is from the person supposedly making it."

Pai's letters say that seven phone providers apparently do "not yet have concrete plans to implement a robust call authentication framework" and asked those carriers to answer a series of questions by November 19. Those carriers are CenturyLink, Charter, Frontier, Sprint, TDS Telecom, US Cellular, and Vonage.