The San Francisco company, which lets people rent spare rooms or entire homes for short periods, will start warning hosts in Paris when they may be violating city regulations, Airbnb announced in a blog post on Thursday. It has agreed to start a four-month test to notify hosts who may be exceeding the 120 day annual limit for short term rentals or renting an apartment that is not their main residence. Both are violation of city rules and carry fines as high as $28,500, according to the Wall Street Journal.

Airbnb won’t disclose any host names to Paris officials. But the city does hope the more aggressive policy is a first step in creating a system to tamp down on illegals rentals.

Airbnb described the new policy as a way “to promote responsible home sharing and help ensure hosting does not negatively impact the availability and affordability of housing in Paris.” It explained that hosts who may be violating the city’s ordinances “will receive a letter from City Hall – sent via Airbnb – reminding them to follow local home sharing rules.”

Get Data Sheet, Fortune’s technology newsletter.

The new pilot is unusual for Airbnb, which so far has strongly resisted helping cities police illegal rentals. It now collects taxes from hosts in a few cities like San Francisco, but does so through specific agreements that prohibit tax collectors from sharing that information with other agencies that are responsible for policing landlords.

Last year, Airbnb also pledged to begin cooperating more with cities, although until now, that promise has only resulted in the company publishing partial data about landlord activity in New York City through its service.

In Paris, where Airbnb has more than 60,000 rental listings, city officials have found a significant number of violations. In December, among 2,000 listings in Paris’ Marais neighborhood, officials found that roughly 100 tourist apartments violated regulations, the city told the Journal.