SIPTU representatives are to meet with Marks and Spencer workers to discuss today's announcement that the company is to close four of its stores.
180 people will lose their jobs when the company closes two stores in Dublin - in Tallaght and Dun Laoghaire, one in Naas in Co Kildare and one in Mullingar in Co Westmeath next week.
The company said the closures are because the stores are unprofitable.
Meanwhile - Superquinn has also announced that it is to be rebranded to SuperValu from early next year - resulting in the loss of 102 office workers.
Musgrave - which owns the supermarket chain - said the 24 shops will be renamed Supervalu from February but certain products will retain the old branding.
SIPTU organiser Neil McGowan said a meeting will take place tomorrow with M&S staff to discuss what options are available to them.
"It's a big shock and people obviously have to go home today and tell their families and friends," he said.
"It's just a very difficult time for everybody
"We are focussing on trying to achieve the best possible range of options available for people who have been impacted by this devastating news."