SAN FRANCISCO — San Francisco’s new crackdown on a mobile app that allows people to auction off their public parking spots marks yet another clash between innovative technologies and regulators trying to maintain law and order, public safety and a sense of social decorum.

The app, called Monkey Parking, allows drivers who score a notoriously hard-to-get San Francisco parking spot to sell it for $5, $10, even $20 and then hang out there until the buyer arrives to take their place.

“It’s illegal, it puts drivers on the hook for $300 fines, and it creates a predatory private market for public parking spaces that San Franciscans will not tolerate,” City Attorney Dennis Herrera said in a statement Monday, ordering the Rome-based tech startup to stop the practice.

Herrera said people are free to rent out their own private driveways and garage spaces but the city “will not abide businesses that hold hostage on-street public parking spots for their own private profit.” Two other startups face similar letters.

State and federal lawmakers have grappled with new technologies that people can use to privately replace taxis, hotels and even restaurants. But nowhere is the conflict tougher than in San Francisco, which Silicon Valley firms often use as a testing ground, pushing the boundaries of local authorities who don’t want to quash the booming tech economy.

Earlier this year, the city ordered Google to move a partially built four-story mystery barge from the middle of the San Francisco Bay after state officials said it was under construction without proper permits.

Police also insist ridesharing services like Uber, Lyft and Sidecar — which gained great traction during Bay Area Rapid Transit strikes last year — are operating illegally when they pick someone up at the airport.

And a possible ballot initiative this fall would charge Airbnb vacation rental app users the city’s 14 percent hotel tax if they want to rent a room in their house to a stranger.

Internet industry analyst Larry Downes said the real problem is that San Francisco’s leaders have made short-sighted policy decisions on housing, development and public transit, leaving the city plagued with dense traffic and costly housing amid a tech boom.