In the past two days, Honolulu has mailed letters to 5,000 owners of suspected illegal short-term vacation rentals. The message: Stop what you’re doing.

The city is gearing up for Aug. 1 when Bill 89, the new law cracking down on short-term rentals, takes effect. No one has received a violation notice yet, but city officials said the “courtesy letters” are a warning.

“We’re hoping this letter will result in a change of behavior,” Mayor Kirk Caldwell said Thursday.

With the exception of non-conforming units grandfathered in from the 1980s, short-term vacation rentals outside of resort zones have been illegal for decades. But the city has failed to enforce its own laws.

Before Bill 89, Department of Planning and Permitting personnel had to catch an illegal rental owner red-handed by deploying inspectors to stake out properties. The department lacked the resources to keep up with the thousands of illegal rentals. That frustrated some who have complained that illegal rental owners profit off tourists who disrupt residential areas and change the character of entire communities.

The new law allows DPP personnel to use rental hosting platforms like Airbnb and VRBO for their enforcement. Properties that are listed for rent for less than 30 days are automatically in violation, regardless of whether they’re actually rented out.

“If you have a vacation rental hosted or unhosted outside a resort area and without a non-conforming use certificate, you’re in violation,” Caldwell said.

DPP Acting Director Kathy Sokugawa said her staff is scanning ads, many of which don’t list specific addresses, and using online and department resources to identify the addresses and find the owners. Caldwell said the city is considering hiring a third-party vendor to help.

“We’re starting a new era of enforcement, and we’re excited about it,” Sokugawa said.

Violators could face fines of up to $10,000 a day.

The new law requires non-compliant rental owners to cancel reservations for August and onward and is leaving some with a difficult choice: sell their property, or list it for long-term renters. Sokugawa said her office received about 100 “hate calls” in the last three days from rental owners who don’t believe they should face enforcement.

The city isn’t going to cut them any slack, Sokugawa said.

“Can we give them a break? The law doesn’t allow for it,” she said.

Caldwell said more properties are already being listed for sale and for long-term leases as a result of the law.

Under Bill 89, the city will legalize 1,700 hosted short-term rentals starting in October 2020. Rental owners will be chosen by lottery and limited in number by district. They will be required to live on the property and register with the city.

Read a sample of the city’s warning letter: