Airbnb hosts in San Francisco may be in for a rude awakening.

Last week San Francisco resident Jeffrey Katz received a 72-hour eviction notice that stated, "You are illegally using the premises as a tourist or transient unit," charging him with violating the city's ordinances.

Katz reportedly contacted Airbnb, but said the company "didn't seem quite interested," SF Gate reports.

"Unfortunately, we can't provide individual legal assistance or review lease agreements for our 500,000 hosts, but we do try to help inform people about these issues," an Airbnb spokesperson tells Business Insider via email. "Countless San Franciscans have been able to pay their bills and stay in the city thanks to Airbnb. People who occasionally share the home in which they live aren't hurting anyone and landlords who seek any excuse to evict tenants so they can raise the rent are only helping themselves."

San Francisco bans short-term rentals, which means that anyone who rents out their space on services like Airbnb and VRBO can face fines by the City Planning Department, and eviction on the grounds of illegally operating hotels.

"Using an apartment for short-term rentals is a crime in San Francisco," Edward Singer, the attorney who filed the notice against Katz, told SF Gate. "It's obviously not the same moral culpability as running a house of prostitution or manufacturing methamphetamines, but any illegal use is grounds for eviction."

For what it's worth, the law is pretty clear (see section 41A.4). In short, San Francisco bans all residential rentals that are shorter than 30 days, unless the host has a permit. Airbnb also warns hosts to check in with their local laws and leases.

Last month, Lisa Weitekamp and Chad Selph also received a 72-hour eviction notice for renting out one of their guest rooms to two Airbnb guests for a total of three nights in October 2013.

For hosts in San Francisco, it's probably best to try to be as discreet as possible with guests. Though, it seems that the law may eventually change down the road. If San Francisco Board of Supervisors President David Chiu has his way, a new law would amend the codes that ban short-term rentals.

"If you live next door or nearby, and all of a sudden a place is turned into a hotel with people coming in and out, generally that is not welcomed by most residents," Christine Haw, SF Planning Department code enforcement manager, told SF Gate.

But it's not just San Francisco hosts who are at risk.

In New York, there's a law that makes it illegal for people to rent out their homes or apartments for less than 29 days. The law is actionable only as a secondary offense, however. For example, if the police show up after a noise complaint and then find that you're renting out your space, that's when you get in trouble.

All eyes are on Airbnb, as it's reportedly raising somewhere between $400 million and $500 million at a $10 billion valuation. That would make Airbnb more valuable than large hotel operators like Wyndham Worldwide Corp, which is valued at $9.4 billion. It would also be more valuable than Hyatt Hotels Corp., which is valued at $8.4 billion.