About a month ago, we wrote about how San Francisco International Airport Director John Martin was cracking down on rideshare drivers  ferrying passengers to the airport.
In a formal letter, Martin enlisted the help of the California Public Utilities Commission to assist with enforcement actions against Uber, Lyft, and other so-called "transportation network providers," whose drivers were found to be taking passengers to the airport despite a state decision requiring them to obtain permits from airport administrators to do so.
The permits haven't yet been obtained because the TNCs took issue with SFO's proposed pilot program, and subsequently refused to fill out the permit applications and send them in .
It appears CPUC President Michael Peevey took Martin's plea for help seriously. In a letter dated June 10, Peevey called on TNCs to cease airport operations until they had secured permits from airport authorities. The letter warns that if the companies do not comply and are found to be in violation of the state's decision governing TNCs, "the CPUC may revoke your permit to operate."
Here's the letter, which references operations in other California cities as well.