The Airbnb internet phenomenon is a boon for tourists, who find accommodation in popular destinations at a fraction of the cost of a hotel. But in some cities the explosion of holiday lets is beginning to cause serious concern. The authorities in Paris are so worried about the drain on residential property that they have enacted drastic measures to bring it under control, reports BBC News.
However, so far few property owners have complied with the new rules.
Under French law you can rent out your flat for short periods to holiday-makers - as long as it is your primary residence.
But City Hall in Paris believes that as many as two-thirds of properties being rented on very short lets are not primary residences.
They are flats that are being used solely for making money via year-round holiday lets, the authorities say. And in the vast majority of cases their owners are flouting the law.
As a result it is estimated that a staggering 20,000 people - foreigners as well as French - are today liable for fines of thousands of euros.
Very short term internet flat rentals have seen a vertiginous increase in the last three or four years, in Paris as well as in cities like New York and Barcelona.
The last study, carried out in 2011, put the number of Paris apartments being let out to tourists at 20,000. Today officials say it has risen to 30,000.
"Holiday lets are an extremely profitable business," explains François Plottin, who runs a team of 20 inspectors at City Hall.
"A small flat can make in a week what it would normally make in a month if it was let out to locals."
"And because of the popularity of Paris as a tourist destination, the occupancy rate is very high. Flats are typically let out for 75 or 80% of the year."
But French law says that the minimum period for letting out a residential property is one year.
To let out a flat for shorter periods requires registering it as a commercial property. And - despite repeated warnings - that is something that only a tiny fraction of owners have bothered to do.
At Airbnb - by far the biggest internet site dealing in holiday lets - they say that the vast majority of their business is with people legally letting primary residences.
The figure offered by Airbnb's Paris director Nicolas Ferrary is 83%. However, that is disputed by François Plottin, who says around half of properties advertised on Airbnb are not primary residences.
"We do everything to comply with the rules, and it is clearly signposted to users of our website what those rules are," says Mr Ferrary.
The repercussions on the Paris residential market are severe, according to Ian Brossat, Director of Housing at City Hall.
"There is already a serious shortage of flats in Paris, especially studios and two-room apartments where couples might start a life together.
"Now we have this growing problem of holiday lets, with investors moving in and buying up as much as they can.
"It has become a business, and the result is fewer properties on the market for ordinary Parisians, and higher prices for what is available."
The holiday let phenomenon is concentrated in big tourist areas like the Latin Quarter and the Marais. Here it is possible to find buildings where multiple flats are being permanently let out to short-stay visitors.