The city's hands are tied: The fee charged to short-term rental hosts, currently $50 for two years, is set to quintuple to $250. That's based on San Francisco's short-term rental legislation, crafted with no shortage of input from industry leader Airbnb. According to the law, the city controller must annually review enforcement costs, then automatically adjust hosting fees to cover them.

That's what SF controller Ben Rosenfield tells the Chronicle, who learned of the news from a memo about the new fees sent out last week. “The way the ordinance is written, there is no discretion for our office” says Rosenfield.

The math goes like this: The six-person Office of Short-Term Rentals has an annual budget of $850,000, and it's levied fines that collect only a quarter of that. To close the gap, the city charges fees to hosts: So far that fee has been $50 for two years, but now that a year of data is available, the controller's office will annually revise the fee, and this time, it's going to have to be $250.

One chief reason for the much higher fee? Lack of registration: Just 1,700 hosts are registered of roughly 10,000 hosts in the city, by the Chronicle's count, meaning that scofflaw hosts are driving up costs for law-abiding ones. That phenomenon feels even more likely to continue with heightened registration fees, as officials themselves admit. “We have a concern about the chilling effect on registrations that such a dramatic increase could have,” Office of Short Term Rentals director Kevin Guy tells the Chronicle. “It’s our preference to keep the fee level to the current $50... Our strong preference is to reward the good actors who want to be registered hosts.”

That could be possible if the Board of Supervisors were to butt in, revising the fee structure. But with that body feuding with San Francisco-based Airbnb, an intervention appears unlikely: Recently, the company sued the city over the Board's decision to directly fine short-term rental platforms like Airbnb and VRBO for listing unregistered units, rather than simply fining hosts.

Meanwhile, Airbnb is set to release a series of new ads in San Francisco, New York, Los Angeles, and Vancouver — battleground areas for short-term rentals —t hat appear to have a similar message to some previous Airbnb ads. No, not those short-lived, passive-aggressive billboards in which Airbnb congratulated itself for finally paying taxes and mocked library hours. Instead, as the company will argue, its very existence makes expensive city living affordable to hosts by offering them extra income.

Related: Airbnb Again At The Center Of Political Play This Election Year As Supervisors Fast-Track Amendments