Construction workers set up a filtering roadblock on the Nantes ring road to protest against rising fuel prices.
Vehicles were slowed as demonstrators handed out leaflets and called for government action.
Protesters say their sector has been overlooked compared to others and are demanding talks with authorities.
According to workers, a sharp rise in diesel costs, combined with a difficult economic year and poor weather, has left many small businesses struggling.
Some say they are now forced to carry out projects with little or no profit, while others warn they may have to cancel jobs due to rising costs.