More than 8,000 drivers, warehouse and support staff at Morrison's distribution depots are to vote in a strike ballot.
The Transport and General Workers Union (TGWU) and GMB yesterday confirmed that they have given the statutory seven days notice to the supermarket chain after failing to get a positive response to their demand for national bargaining.
The Bradford based supermarket completed the take over of Safeway in 2003. The deal worth £ 2.3 billion, brought together the UK's fourth and fifth largest supermarket groups.
The strike could potentially see the supermarket short of goods to fill its shelves.
Brian Revell, national officer of the TGWU, said the merger of Safeway into Morrison's had caused "no end of problems" for workers.
"We believe the best way to deal with the situation would be to stop being in denial, as Morrison's appear to be, and agree to work with the unions to provide a national framework so we can address issues collectively."
Jude Brimble, GMB national officer, said, "Our members have had enough of the 'Morrison Way'.
"They were happy under the Safeway management but cannot abide the chaotic Morrison's style that seeks to cut pay and corners and undermine the long-term stability of the company."
The two unions believe that negotiations should be on a national basis, but Morrison's has argued that it cannot enter national negotiations because it is still integrating the Safeway store portfolio.
A spokesman for Morrison's said: "We are ready to meet with the unions. But most of the issues we are dealing with are local, so we are not able to deal with the unions on a national basis."
The TGWU and the GMB said their members will vote from next Wednesday with the result expected on August 31.