BARCELONA—The newly elected leftist mayor of Spain’s second city imposed a freeze on licensing new tourist accommodation in an effort to control the growth of an industry that is causing social disruption even as it cushions the effect of Europe’s economic crisis.

Mayor Ada Colau said Thursday’s freeze, which she expects to last a year but could be extended, will halt 30 projects that were in the process of being licensed, including some significant hotel investments.

Barcelona, one of Europe’s top vacation destinations, needs to put a brake on development and “begin a process of participatory reflection instead of going around putting out fires,” she said on Thursday, adding “It was a priority to impose order. Up to now, tourist policy has been handled with patches.”

Last year, Barcelona received roughly 7.5 million international visitors, more than four times the city’s population. The number of tourist rooms available in Barcelona has roughly doubled to some 70,000 over the past 12 years. That doesn’t include a growing number of unlicensed rooms, including many private apartments rented out by their owners.

Last summer, protests broke out in some neighborhoods amid complaints of excessive noise, overcrowding and bad behavior by visitors. Ms. Colau, who was elected in May at the head of a coalition including the far-left Podemos Party, said during the campaign that Barcelona ran the risk of being as overrun with tourists as Venice is, and pledged to bring growth under control.