Several top teams on Friday pulled out of the Etoile de Besseges cycling race in France citing safety concerns over traffic management on the course for a second straight day.
The peloton dismounted just after midday when a vehicle appeared on a roundabout.
Several teams disagreed with the resumption of the race and returned directly to their buses.
"Our team is one of the several that have decided to retire from today's stage due to several incidents over motor vehicles being allowed onto the race course," the Soudal Quick-Step Pro Cycling Team said.
"We find this unacceptable and decided not to rejoin the stage as we prioritise the safety of our rides and staff."
Soudal's French rider Paul Magnier had been leading the five-day race around Besseges in southern France.
The Ineos, Lidl-Trek, Uno-X and EF Education teams also ceased their participation.
A similar incident took place on Thursday provoking an accident which forced Belgian race favourite Maxim Van Gils of Bora-Red Bull to retire with a right hip and right wrist injury.
The riders have designated three representatives to discuss their concerns with race management and cycling governing body UCI commissioners.