Officials at the San Francisco International Airport (SFO) say they have been making citizen arrests of rideshare drivers throughout July. Airport spokesperson Doug Yakel told Ars on Tuesday that airport officials have made 12 such arrests since July 10.

Rideshare companies like Uber, Lyft, and Sidecar use mobile apps to help city dwellers find rides in areas where cabs are scarce or expensive. But taxi service is heavily regulated in big cities nationwide, and rideshare companies have ruffled feathers by operating outside of traditional restraints placed on taxi drivers.

Cities like New York and Chicago have made it difficult for rideshare companies to operate, and the California Public Utilities Commission (CPUC) slapped Uber, Lyft, and Sidecar with $20,000 fines in November 2012 (although the commission later rescinded the fines). In December of last year, the CPUC issued a proposal for examining the legality of the rideshare services, and the commission is expected to revisit the issue sometime this week.

In the meantime, rideshare services, excluding Uber, which says it is properly licensed by the CPUC, have been operating in California in a legal gray area. Still, SFO issued a cease and desist order banning Uber, Lyft, Sidecar, and other rideshare services from airport premises in April. After the cease and desist order was issued, airport officials and police began “admonishing” rideshare drivers who dropped off or picked up passengers at the airport, according to CBS San Francisco.

Starting July 10, airport officials began slapping rideshare operators with citizen arrests for trespassing when they were discovered at the airport. “This is not the type of arrest where somebody gets put in jail,” Doug Yakel told Ars. “It's a misdemeanor and it's for trespassing.” Yakel went on to say that the curbside airport police observe and “have the right to question drivers,” if they see anything that appears to indicate ridesharing. Tells include anything from the giant pink mustache that Lyft drivers slap on their car grill to seeing the rider and driver exchange money before the rider leaves. “There could be a variety of different things that [airport police] would be looking for to see if there's a rideshare transaction,” Yakel explained.

At that point, airport police contact an airport official, who writes the rideshare driver a citation for a court date. Yakel said that officials are writing citations under California Penal Code section 602.4, which states that people offering “goods, merchandise, property, or services of any kind whatsoever” on airport property, without the airport's permission, are guilty of a misdemeanor. Yakel told Ars that he didn't know how high the fine for such a misdemeanor might be.

In response to the news of the arrests, Sidecar e-mailed its drivers a warning this morning [emphasis theirs]:

We want to let you know that we are working hard to get this situation resolved ASAP. In the meantime and until the situation is resolved, we are advising that you avoid trips to SFO.

An Uber spokesperson told Ars in an e-mail on Tuesday that "all Uber partners and their drivers utilizing the Uber platform are properly licensed and regulated per the California PUC." The company claimed it does not "know of a single instance of SFO authorities arresting any driver connected to the Uber platform."

The Uber spokesperson went on to write that, "Earlier in the day, the [airport] spokesperson was saying [that] drivers working with Uber had been arrested at SFO. We believe those statements to be false. We will check into whether any drivers have been cited... But if any have, we look forward to a court date so that SFO's abuse of power and public trust can be publicly exposed."

A representative from Lyft was not immediately available for comment.