The city council of Barcelona has a message for tourists who want to visit and stay in a homeshare or vacation rental: Make sure it’s properly licensed first.

A social media campaign and accompanying website sponsored by the Catalonian government is encouraging visitors to check if the vacation listing they want to rent is legally registered with the city. It also encourages locals to report flats they believe are being rented out illegally. The online process for tourists can be done entirely in the English language. Naturally, there is a hashtag too: #fairtourismBCN

In keeping with a wider trend in Spain, Barcelona has been on the vanguard of issuing restrictions for Airbnb and similar sites for several years now. In 2011, the region of Cataluña created the license that all legal vacation rentals must now bear, known as the HUT license. Then in 2014, it stopped issuing new licenses completely; at present, there are 9,600 apartments in the city that are property licensed. Housing councilor Janet Sanz recently told the Guardianthey don’t have a plan to issue new licenses any time soon—effectively putting a cap on the vacation rental market.

The government says they’ve shut down as many as 2,000 illegal listings with beefed up enforcement teams. They also reached an agreement with Airbnb to remove illegal listings from its platform following a protracted battle and levying a yet-to-be-paid €600,000 fine. However, officials believe their work is not done, as many other sites also advertise vacation rentals illegally.

As the the government’s fairtourism website states:

Unfortunately, for all its legal accommodation available, Barcelona also has a range of illegal accommodation that harms not just the people who rent it – depriving them of their right to complain about any incidents and denying them the supplementary services they are otherwise entitled to – but also the city itself, as it creates speculation and illicit economies and its activities leave nothing positive for local neighbors, causing nuisance and complaints.

If you are visiting Barcelona, we need your commitment and cooperation to prevent the proliferation of this illicit economy in our city and the irresponsible, economically unsustainable and environmentally unfriendly tourism it encourages.

As has been well documented, while the “live like a local” travel ethos enabled by the internet era has served adventure-hungry travelers, it hasn’t always been so great for actual locals. Use of the fairtourism website is not mandatory, of course, but it’s clear case of city officials putting some of the responsibility for responsible tourism in the hands of tourists—not just travel companies like Airbnb or tourism operators.

In terms of the seemingly intractable battle against over-tourism, appealing to travelers sense of ethics s a notable step—and one that travelers should watch out for other cities to emulate.

Quartz has reached out to Airbnb and will update this post if they respond.