The refinery, owned by Federated Cooperatives Ltd, tweeted on Tuesday that it had issued a 48-hour lockout notice to 800 workers in the interest of public safety, after their union issued a strike notice. Talks had broken down over pensions.
The refinery was running on Wednesday at full operation, spokesman Brad DeLorey said in an email. Co-op built a work camp in autumn in case of a labor disruption and intends to keep it operating with managers and contractors.
The Co-op Refinery has capacity to process 135,000 barrels of oil per day.
Unifor Local 594 could not be reached. Workers voted overwhelmingly to strike earlier this week.
The lockout comes as Western Canadian oil producers in Saskatchewan and Alberta struggle to move crude to U.S. refiners, their main market, due to congested pipelines. Co-op Refinery makes gasoline, propane and asphalt, among other products.