Union leaders say Superstore outlets in Alberta will face a consumer boycott if its workers end up going on strike Sunday over a contract dispute.

Public and private sector unions representing about 250,000 Alberta workers say they have sent a letter to Loblaw Companies Ltd. CEO Galen Weston Jr.

The letter calls on the company to present a reasonable offer to its 8,500 Alberta employees represented by the United Food and Commercial Workers union.

Union members can legally walk off the job early Sunday morning to press contract demands.

The Alberta Federal of Labour and the other labour groups say they will actively encourage their members not to shop at Superstore if a deal isn't reached.

Others involved in the boycott threat include the Alberta Union of Provincial Employees, United Nurses of Alberta, Health Sciences Association of Alberta, Unifor and the Canadian Union of Public Employees.