Police had to remove bales of hay blocking the road 26 kilometres (16 miles) into the day’s ride from Carcassone as farmers demonstrated against a cut in state aid.
Among the riders affected by the tear gas was Team Sky’s overall leader Geraint Thomas, who was pictured rubbing his nose following the incident.
Television images showed Tour de France medical officers handing out eye drops to riders including green jersey points leader Peter Sagan.
The 218km stage with a finish in Bagneres-de-Luchon and featuring two first category climbs in the Pyrenees restarted at 12:36 pm (1036 GMT) after an interruption lasting around 10 minutes.
This year’s Tour de France has been marked by a series of incidents on the sidelines of the race including abuse directed at Team Sky and its leader Chris Froome.
Amid a general feeling of suspicion surrounding Sky and their sheer domination of the race, Froome has been spat at and manhandled, Thomas has been booed off the podium and some of Sky’s staff have also faced abuse.