EDMONTON - 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.

"In the event of a strike, we will communicate our concerns about your company's labour relations practices to our members and actively encourage them to not shop at Superstore until a fair agreement has been reached," AFL president Gil McGowan said in a release Friday.

"In an economy as vibrant as Alberta's, there is simply no excuse to shortchange the employees whose efforts make your business thrive."

The main issues in the dispute include wages and reduced hours for Superstore's mostly part-time workforce.

Superstore workers in Saskatchewan and Manitoba reached tentative agreements with Loblaw in recent weeks after voting in favour of going on strike.

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  • Alberta sheriffs take part in a strike as they joined correction guards, setting up a picket line outside the Edmonton courthouse in Edmonton, Alberta on Monday April 29, 2013.THE CANADIAN PRESS/Jason Franson

  • Alberta sheriffs take part in a strike as they joined correction guards, setting up a picket line outside the Edmonton courthouse in Edmonton, Alberta on Monday April 29, 2013.THE CANADIAN PRESS/Jason Franson

  • Alberta sheriffs take part in a strike as they joined correction guards, setting up a picket line outside the Edmonton courthouse in Edmonton, Alberta on Monday April 29, 2013.THE CANADIAN PRESS/Jason Franson

  • Alberta sheriffs stay dry in a tent while taking part in a strike as they joined correction guards, setting up a picket line outside the Edmonton courthouse in Edmonton, Alberta on Monday April 29, 2013.THE CANADIAN PRESS/Jason Franson

  • Alberta sheriffs take to the streets and join correction guards, setting up a picket line outside the Edmonton courthouse in Edmonton, Alberta on Monday April 29, 2013. THE CANADIAN PRESS/Jason Franson

  • Clerks and Alberta sheriffs joined striking correction guards today, setting up a picket line outside the Edmonton courthouse in Edmonton, Alberta on Monday April 29, 2013.THE CANADIAN PRESS/Jason Franson

  • The Edmonton Remand Centre is shown on Saturday April 27, 2013. Alberta's deputy premier says a labour dispute where guards at provincial jails have walked off the job has resulted in inmates trashing the inside of Edmonton's new remand centre. THE CANADIAN PRESS/Ben Lemphers

  • Correctional officers take part in a strike at the Edmonton Remand Centre on Saturday April 27, 2013. Alberta's deputy premier says a labour dispute where guards at provincial jails have walked off the job has resulted in inmates trashing the inside of Edmonton's new remand centre. THE CANADIAN PRESS/Ben Lemphers

  • Correctional officers take part in a strike at the Calgary Correctional Centre in Calgary on Saturday April 27, 2013. Workers at detention centres in Alberta have walked off the job, engaging in what the province's justice minister is calling an "illegal job action". THE CANADIAN PRESS/Jason Franson

  • Correctional officers take part in a strike at the Calgary Correctional Centre in Calgary on Saturday April 27, 2013. Workers at detention centres in Alberta have walked off the job, engaging in what the province's justice minister is calling an "illegal job action". THE CANADIAN PRESS/Jason Franson

  • Correctional officers take part in a strike at the Calgary Correctional Centre in Calgary on Saturday April 27, 2013. Workers at detention centres in Alberta have walked off the job, engaging in what the province's justice minister is calling an "illegal job action". THE CANADIAN PRESS/Jason Franson

  • Correctional officers take part in a strike at the Edmonton Remand Centre on Saturday April 27, 2013. Alberta's deputy premier says a labour dispute where guards at provincial jails have walked off the job has resulted in inmates trashing the inside of Edmonton's new remand centre. THE CANADIAN PRESS/Ben Lemphers

  • <strong>NEXT ----> Air Canada wildcat strike</strong>

  • Wildcat Strike

    A man spits onto the face of an Air Canada baggage handler during a wildcat walkout at Toronto's Pearson International Airport early Friday March 23, causing some flights to be delayed. The job action began Thursday evening and left hundreds of passengers in limbo after they had to disembark from several flights already on the tarmac and head back to the terminal. Shortly after the man was removed from the area by police. THE CANADIAN PRESS

  • Wildcat Strike

    Police remove a person from the area as Air Canada baggage handlers stand outside during a a wildcat walkout at Toronto's Pearson International Airport early Friday March 23, causing some flights to be delayed. The job action began Thursday evening and left hundreds of passengers in limbo after they had to disembark from several flights already on the tarmac and head back to the terminal. (AP Photo/Victor Biro, The Canadian Press)

  • Wildcat Strike

    A police officer looks on as Air Canada baggage handlers stand outside during a a wildcat walkout at Toronto's Pearson International Airport early Friday March 23, 2012 causing some flights to be delayed. The job action began Thursday evening and left hundreds of passengers in limbo after they had to disembark from several flights already on the tarmac and head back to the terminal. (AP Photo/Victor Biro, The Canadian Press)

  • Wildcat Strike

    Air Canada baggage handlers hold a wildcat strike at Toronto Pearson Airport early Friday March 23, 2012. THE CANADIAN PRESS/Aaron Vincent Elkaim

  • Wildcat Strike

    Air Canada baggage handlers hold a wildcat strike at Toronto Pearson Airport early Friday March 23, 2012. THE CANADIAN PRESS/Aaron Vincent Elkaim

  • Air Canada baggage handlers hold a wildcat strike at Toronto Pearson International Airport early Friday, March 23, 2012, in Toronto. Air Canada canceled more than two dozen flights to Canadian and U.S. destinations early Friday as a wildcat strike by its ground workers threatened to create travel chaos at Pearson airport. (AP Photo/The Canadian Press, Aaron Vincent Elkaim)

  • Air Canada baggage handlers hold a wildcat strike at Toronto Pearson International Airport early Friday, March 23, 2012, in Toronto. Air Canada canceled more than two dozen flights to Canadian and U.S. destinations early Friday as a wildcat strike by its ground workers threatened to create travel chaos at Pearson airport. (AP Photo/The Canadian Press, Aaron Vincent Elkaim)