The city of Minneapolis has mailed 731 letters to residents who list their homes as short-term rentals on sites such as Airbnb, warning them that if they do not either remove the listing or pay a registration fee, they could face a $500 fine.

The city is giving homeowners six weeks to comply with an ordinance passed in October that requires people who rent out their homes and the online platforms that advertise the properties to apply for municipal licenses and renew them each year. More than 3,000 properties in the city are listed on online rental platforms.

For those who rent out a room in their home but continue to live in it, no registration is required.

Those who rent out their whole home when they’re away must pay $46 per year for a license and may be subject to inspections. Those who rent out a home they don’t live in must get the same type of rental license required for a conventional landlord, and those licenses start at $70 per year.

Rental platforms such as Airbnb, HomeAway Family and TripAdvisor must also be licensed by the city. Those that post 150 dwellings or fewer must pay a $630 annual fee. Larger platforms, such as Airbnb, must pay $5,000. Airbnb has 2,610 listings in Minneapolis and HomeAway Family has 331, according to the city’s Department of Regulatory Services.

The rules went into effect in December as the number of Airbnb-type listings in Minneapolis rose dramatically ahead of the Super Bowl.

So far, 327 residents have registered their homes as short-term rentals, and another 33 have received short-term rental licenses.

The number of listings changes constantly. The city uses an outside company to monitor short-term rentals for compliance. Validation technicians review listings against municipal records, social media and open-source maps (such as Google street view) to confirm addresses and property owners.

The outside firm is working to validate more homes that are not in compliance with the ordinance and is checking more than two dozen other rental platforms in addition to Airbnb, HomeAway Family and TripAdvisor.

Mayor Jacob Frey authored the Minneapolis ordinance when he was a council member. Council Member Andrew Johnson cast the lone vote in opposition.