As previously reported, California’s regulatory bodies have been trying to find a way to work with ride sharing services like Uber, Sidecar and Lyft. Now SFO’s getting in on the cease and desist game, citing overcrowding and lack of permits as a reason to ban the company’s drivers from the airport.

Though the CA PUC’s cease and desist order has been suspended regarding donation-based rideshare company Lyft and ultra-snazzy town car pickup service Uber, SFO has apparently picked up their slack and issued their own cease and desist letters to SideCar Technologies Inc, InstantCab, Tickengo, FlightCar (which lets people parked at the airport to rent their car out to other drivers), the aforementioned Uber and the operator of Lyft, Zimride.

SFO airport spokesman Doug Yakel told the SF Business Times that the letters, which were sent February 28, were responding to issues of fairness and space. Yakel pointed to the many existing, legal, and permitted transit options.

“We’re certainly open to new business concepts, but we want to apply the same standard to all businesses that operate here at SFO and that requires going through the permit process,” Yakel told KCBS.

As of press time, only SideCar and InstantCab had posted responses to the SFO letter.

In their blog post, Instacab “re-imagines” the letter they received from SFO, before posting the actual letter from SFO to the company, which states “the continued operation of any Instantcab community driver services at SFO is an unlawful trespass.”

However, according to Instacab, “The Airport notice also does not affect our taxi drivers — they can still drop off our customers at the airport.”

Sidecar takes a similarly defiant stance, saying that “We’re going to defend the right to share resources to regulators, in court, to SFO and anyone else who stands in the path of innovation.”