Though many critics have called the "Airbnb law" that the SF Board of Supervisors passed last year unenforceable, enforcement appears to be ramping up, especially after this past election in which short-term rentals were one of the biggest hot-button issues. Prop F may have failed at the ballot box, but the mayor and his staff clearly know that residents are passionate about the issue of housing stock being taken off the market, and as CBS 5 reports, the policing of short-term rental hosts who appear to be renting out homes that are not their primary residences is well underway.

Kevin Guy, the head of the new Office of Short-Term Rentals at City Hall, says that so far he and his team have issued $400,000 in penalties to 37 different properties, with 20 more under investigation.

The primary violation the office is going after is the illegal conversion of housing units to full-time transient use. Under the existing law, homeowners are limited to renting entire units for 90 days or less per year, and these must be their primary residences. If hosts are renting only single rooms, there is no limit.

Without being given access to data from Airbnb about rental days, people have wondered how the city was going to police the 90-day limit. Airbnb has earlier claimed that 90 days is about average for the vast majority of their hosts, though competing reports have come up with competing numbers of how many units are being rented on a short-term basis full-time across the city  by David Campos's estimate, it's in the 2,000 range, while Airbnb doesn't give a hard number, but stressed that it would take an average of 211 rental nights to make the equivalent of what a unit's annual, long-term rent would be.

Guy explains that their first line of investigation is going after those who've registered more than one short-term rental in their name, meaning that both can't be their primary residence  they obviously can't yet go after those violators who haven't bothered registering with the city. Subsequent investigation by CBS 5 has revealed "plenty of lockboxes, keyless doors, and neighbors who knew exactly why we were there," citing units that were sold and immediately appeared to have a revolving door of out-of-town guests.

So, while 57 units may just be a drop in the bucket, kind of like IRS audits, it's these examples that may encourage homeowners to be more honest. Violators have reportedly received orange notices on their doors which mark the start of the penalty time clock ticking  CBS 5 reached one homeowner who admitted they'd broken the rules and had paid their fine, and they spoke to another on the record, Betsy Brill, who said she hadn't broken any rules, and that she and her husband rented out their primary residence when they were traveling.

The latest batch of alleged violators are in Telegraph Hill, North Beach, Potrero Hill, Cole Valley, and The Haight, but not in the ever popular Mission where there are likely to be many more.

Previously: Just How Many Apartments In SF Are Being Used As Full-Time Airbnb Rentals?