The refinery's North and South LIU amine units will be affected, as well as the refinery's furnace, according to one of the sources.

The shutdown could affect 60-70% of capacity at the plant, which came under new ownership on Monday when the Canadian energy company closed its acquisition of Husky Energy.

Cenovus did not respond to a request for comment.

(Reporting by Laura Sanicola; Editing by Leslie Adler)