The Federal Communications Commission’s war on robocallers continues, with the agency sending cease & desists to more providers.

The FCC passed rules requiring phone carriers to implement the STIR/SHAKEN protocol in an effort to fight robocalls. The protocol allows carriers to verify the authenticity of a caller, pass that verification on to the next carrier for confirmation, and so on. Carriers were given a deadline to implement the protocol or be blacklisted, with the first such carrier blocked in November.

The FCC has now sent cease & desist orders to two additional companies the agency says has been supporting “illegal robocall traffic.” This brings the number of cease & desists to twenty, with the majority complying and cutting off robocall assistance.

The latest cease & desists, sent to SIPphony LLC and Vultik, Inc, included a warning that their traffic could be permanently blocked by downstream providers if they failed to comply.

“You should investigate the identified traffic and take the steps …, including blocking the traffic if necessary, and take steps to prevent your network from continuing to be a source of apparently illegal robocalls,” wrote FCC Enforcement Bureau Chief Loyaan A. Egal. “Failure to comply with the steps outlined in this letter may result in downstream voice service providers blocking all of [SIPphony LLC and Vultik, Inc] traffic, permanently.”

“Scam robocalls are more than just a nuisance, they waste our time and resources and destroy trust in our communications networks,” said FCC Chairwoman Jessica Rosenworcel. “We will continue to use every tool we have to go after this fraud and stop the bad actors responsible for these calls in their tracks.”