Port Elizabeth police said truck drivers were pulling fellow trucks drivers off the N2 near the Coega Industrial Development Zone outside the city since around 10 am on Sunday.
Spokesperson Captain Andre Beetge told Algoa FM News that it was believed that the truck drivers were having in-house issues over employment.
He said police were at the scene to monitor the situation, and that the road was open to traffic.
Beetge said it was a peaceful demonstration, and no incidents of violence had been reported.