The Suncor Energy refinery in Sarnia is in the midst of an eight-week period of planned maintenance.
About 350 employees and contractors are involved in the project.
The company said every effort will be made to ensure disruptions from the maintenance work are kept to a minimum.
The 98,000-barrel-per-day refinery produces gasoline, diesel fuel and paving-grade asphalt and recently underwent a $1-billion investment in new equipment.
