The loading-unloading work has been affected in the plant because of the incident.
The clash occurred as both the Indian National Trinamool Trade Union Congress (INTTUC) factions -- one headed by Milan Mondal and another by Azizul Rahaman -- tried to capture plum posts.
Seven persons from both the sides were injured in the clash. They have been hospitalised and under treatment, police said.
Meanwhile, Rahaman's side alleged that one of its members has gone missing.