Superquinn has confirmed it is to shed 400 jobs and close its Dundalk store.
67 jobs will be lost in Dundalk, with the remaining jobs lost across the rest of the chain from senior management down.
Superquinn has 24 stores in all - today's redundancy announcement is the equivalent of 12% of its staff.
In addition to the job losses, Superquinn said it is looking for remaining staff to agree to more flexible working terms and conditions to protect their jobs and secure the future of the chain.
CEO Simon Burke says that most of the job losses will be amongst full-time staff.
The Mandate trade union, which represents the majority of Superquinn workers, said it was shocked and disappointed by the announcement.
But Mandate Assistant General Secretary Gerry Light said it would be wrong to say they were entirely surprised given the current economic circumstances and the the impact of the cross-border shopping.
Cross-border shopping 'impacting jobs'
He said the fact that it is Dundalk that is the store to close is not without significance.
Mr Light said that for workers in Dundalk the reality of cross-border shopping has come home to roost today.
He said he was now calling on the public and the Government to stop talking about the potential consequences of cross-border shopping and to start looking at the realities and to act accordingly.
Commenting on the job losses, John Ruddy, Editor of Checkout Publications, said customers were moving towards more value-focused chains.
He said 'the whole grocery industry needs to refocus itself and look and say, 'how are we providing value to the consumer?'
Referring to cross-border grocery shopping, Mr Ruddy said: 'People have to realise that if they shop in Newry, if they shop in the north of Ireland, it does have an impact on jobs.
'Maybe people are saying that 'it's nothing to do with me', but it all does matter, it all does count at the end of the day.
'The announcement today is sad proof that that actually is the case,' he said.