The government has cracked down on some robocallers, even going so far as to fine one alleged robocaller $100 million.

But for a long time, companies that allow robocallers to use their services have been left to do their thing — and in the process unleashed billions of robocalls on the annoyed public. The involvement of many voice-over-IP — internet-based phone — companies in enabling robocalling has been a dirty secret in the telecom industry.

Recently, the government has begun to crack down on companies that enable bad actors to scam and harass. This week, the Federal Communications Commission sent letters to six phone companies asking them to stop allowing international robocalls to enter the U.S., and to participate in traceback efforts to track down the sources.

This follows actions from the Department of Justice and the Federal Trade Commission in reining in the companies that facilitate international robocalls.

“The last couple months have been a tremendous breakthrough in government enforcement,” Patrick Halley, of USTelecom, told Yahoo Finance. USTelecom runs the Industry Traceback Group, which consists of 30 telecom companies that trace origins of illegal robocalls. (Yahoo Finance’s parent company Verizon, is a member of this trade group.)

Halley said a paradigm shift is happening in the fight against robocalls.

“What you’re starting to see now is the government, federal and state, pay close attention to the originating voice providers who enable calls made in the face of evidence that the calls are illegal,” he said. “That’s a sea change.”

International calls

Plenty of robocalls are domestic, but many come from abroad. Those callers need a way to get on U.S. networks, and a telecom company that is unable or unwilling to enforce the rules is a way to do so.

This week, the FCC Enforcement Bureau Chief Rosemary Harold sent letters to All Access, Globex, Piratel, Talkie, Telcast, ThinQ, and Third Base, telling them they were used by robocallers as a “gateway into the U.S. telephone network,” according to USTelecom’s traceback program. Last year, the program tracked down 1,000 robocalling sources that represented over 1 million robocalls each, according to Halley.

The letter added that these companies are “uniquely situated to assist government and industry efforts to combat spam robocalls,” which likely involve fake Social Security scams and other harmful practices.

The FCC is also requesting more information about how the companies facilitate international robocalls, whether these companies are doing anything to prevent robocalls, or are tacitly or even unsubtly endorsing this type of behavior, posing questions like: “Does All Access Telecom advertise its services in foreign countries?”