Herrera's letter was the latest as state and federal lawmakers grapple with new technologies that people can use to privately replace taxis, hotels and even restaurants. Firms in neighboring Silicon Valley often use San Francisco as a testing ground, pushing the boundaries of local authorities who don't want to quash the booming tech economy.
Herrera also cracked down on two similar smartphone apps that exchange money for parking spaces.
Two weeks ago, Dobrowolny said MonkeyParking doesn't sell parking spots, but rather convenience, citing freedom of speech. He said people have the right to tell others they're leaving a parking spot and get paid for it.
On Thursday, the company reiterated a similar sentiment in its blog.
"Street parking is currently not a first-come-first-served process, but still a random-served one: you can go in circles for hours while a lucky driver can find a spot in a minute, right in front of you," the blog said. "It is an old and painful problem and we believe that drivers deserve a better solution."