The workers are on strike since December 11 over their unpaid salaries for past four months.
The government appointed management had agreed to pay the workers on Wednesday but there was no sign that it made good on its promise.
The factory's security forces were ordered to drive away the protesters which made the workers angry. Despite attempts, the forces were not able to remove the workers and the stand off between the management and workers continued.
Hegmataneh Industries Petrochemical Company (HIPC) was established in 2002.The plant is located in the province of Hamedan in western Iran.