The scarcity of affordable social housing is a major problem for some of the world’s biggest cities. What makes this issue extremely frustrating is that there’s a decent number of empty properties in these cities that could help solve the problem. Drawing from this frustration, Barcelona – Spain’s second most populous city – has long threatened to fine landlords if they don’t find tenants for their empty buildings.

The tone emerged as the city’s affordable housing crisis deepened, exacerbated in part by the fact that some properties lie vacant even as housing has become more scarce. This month, however, the city has gone further than ever before to act on its threat, levying fines of $3.17 million against two investment funds that each own an unoccupied building in Barcelona’s center. The city’s overall mission is to produce funds that will ensure that other previously empty homes are converted into affordable housing.