On Sunday, dozens of riders suffered punctures while descending at about 70kmh from the Mur de Peguere after carpet tacks had been thrown on to the road.
Tour organisers said they had filed a complaint against "persons unknown" and the National Gendamerie said it had opened an investigation.
Defending champion Cadel Evans was one of the victims, puncturing three times before eventually finishing in the favourites' group after yellow jersey holder Bradley Wiggins, sensing something was amiss, had slowed down the peloton.
“"It's a criminal act, I think you're taking peoples lives in your hands and creating a very dangerous situation," Evans's BMC team general manager Jim Ochowicz, who added to the chaos when he slipped into a ditch trying to assist his rider, told reporters.
"“Someone made a very stupid decision to put tacks on the road in a downhill where he was taking the lives of other people in his hands."
Wiggins said there was nothing the riders could do.
"(Tour competition director) Jean-Francois Pescheux showed me the tacks and I told him what can we do? That's something we have to put up with as bike riders. It's sad," said Wiggins.
“"We're just riders at the end of the day. I hope that's not going to continue. We just have to get on with it really."
Hundreds of thousands of spectators line the roads on every Tour de France stage and the riders are separated from them by barriers only in the final kilometres.
SPORTSMANLIKE GESTURE
“"If that had happened in a football stadium, you'd be arrested or caught on CCTV. We're quite vulnerable at times, being so close to the public. We're there to be shot at, literally." Wiggins said.
Three years ago, two Tour de France riders, Spain's Oscar Freire and New Zealand's Julian Dean, sustained minor injuries after being shot at in an air rifle attack.
Wiggins later told Eurosport there had been plenty of policd around.
"There's enough police on the course to round them up and send them to football matches or something," he said.
Evans, who sits in fourth place overall and could have definitely lost the title because of the incident, said it had happened to him before.
“"This has happened to me before, twice in Spain, that's why I don't race in Spain very often, sorry for the good Spanish people and my Spanish friends and people in Spain who support me but there's a few people who just take things too far," he told reporters.
“"It cost me a Vuelta and cost me other races," he said in an apparent reference to the 2009 Vuelta a Espana which he lost partly because of a puncture.
This time, however, Evans benefited from Wiggins's sportsmanlike gesture as the Briton had the bunch slow down to wait for the Australian.
“"It's pretty obvious that when something like that happens, it's not bike racing. I think fair play to Bradley, it was a very sportsmanlike gesture as far as I can tell," Team Sky principal David Brailsford told reporters.
"“It was the right thing to do, when those incidents happen in sports, you never know what's going to happen to you. What comes around goes around."
Frenchman Pierre Rolland, who is ninth overall, attacked in the descent after Evans's first puncture, prompting podium contenders Juergen van den Broeck and Vincenzo Nibali's Lotto and Liquigas teams to break the truce and increase the pace.
“"What followed was a ride on the front by Lotto and Liquigas much to the annoyance of the BMC team," said Team Sky sports director Sean Yates. "“It was a bit unsportsmanlike."
Rolland later apologised for his move, saying he had no idea something had gone wrong.
“I respect the codes of the peloton. I did not know what was going on. However, I'm really sorry," he told French TV.
