Climbing Mont Blanc, the highest peak in Europe, without having booked a room in a shelter could now get you two years in prison and a 300,000-euro fine under new rules to tackle overcrowding and safety concerns.
At 4,807 metres, the Alpine peak is Western Europe's tallest mountain, attracting more than 20,000 climbers every year.
New access rules
But French authorities say "huge visitor numbers" and people camping illegally have led to concerns over sanitary risks such as water availability and problems with waste disposal.
Starting Saturday, people hoping to scale the mountain via the standard route, which takes several days, must now book a room in one of three shelters. The decree lists them as Gouter, Tete Rousse and Nid D'aigle refuges.
This was essential to "prevent trouble" from climbers who had not booked in advance, the decree said.
The new rules will be in effect until the end of the climbing season in September.
Mountaineers caught camping on the route risk two years in prison and a 300,000-euro fine, said regional administrator Pierre Lambert.
Enjoying Mont Blanc
The decree was signed on the same day a 25-year-old Slovak climber died after falling around 250 metres at the start of that standard route, widely known as the "Route Royale".
During last year's climbing season, fifteen climbers died on Mont Blanc, prompting officials to start limiting access to the most popular route up in July.
But a public information campaign launched last summer to dissuade crowds had proved "ineffective", said Lambert.
The ban marked "the result of 15 years of fighting to make sure mountaineers can enjoy Mont Blanc, while also respecting it", said Jean-Marc Peillex, mayor of the town of Saint-Gervais, where most climbers begin their ascent.
The new rules come as a traffic jam of climbers in the Everest "death zone" has been blamed for two of four new deaths reported on Friday on the world's highest peak.
Eight people have died on Everest in a week with concerns that the drive for profits is trumping safety there.