A strike is under way at nine stores owned by Loblaw in southwestern Ontario.
Workers walked out at midnight at three Zehrs and Real Canadian Superstore outlets in Windsor, Kingsville, Chatham, Leamingston and Sarnia.
Loblaw says all nine stores will remain open, but with modified store hours (10 a.m. to 8 p.m.) and a reduction of some in-store services.
The company says another 60 stores represented by United Food and Commercial Workers union Local 1000A are set to go on strike on Sunday in markets from London to Ottawa.
The union has said the main issues in the dispute are wages, work schedules and benefits.