Lidl has sacked a worker who questioned the supermarket chain's pay policy on Facebook, the trade union Unite claims.
The company announced last month that it would give its staff a pay rise in England, Scotland and Wales - but the 600 Northern Ireland workers would not receive the same 'Living Wage'.
Now Unite claims a staff member here has been dismissed over "breach of confidentiality" after he posted a comment on Facebook questioning the policy.
Lidl says Unite's version of events "contains factual inaccuracies", but the company said it could not comment on details regarding individual employees.
The union's Regional Officer Susan Fitzgerald said: “The decision to dismiss this worker will have a devastating impact on the young person concerned.
"His only crime was to post comments on Facebook questioning the fairness of Lidl pay policy, referencing details already in the public domain."
She said the man, aged in his mid-twenties, did not post anything offensive - but only highlighted the difference in wages between Northern Ireland and the rest of the UK before asking: "Are we being discriminated against?"
Ms Fitzgerald said the decision by management was "vindictive": "They know there is a widespread public revulsion over their unfair policy of paying workers in Northern Ireland less than they do workers in England, Scotland and Wales. This decision will only exacerbate that.
“There is no legal or moral justification for paying workers in Northern Ireland less than workers who do the same work in Britain."
A Lidl spokeswoman said: "This case is part of an on-going disciplinary process which first began over six months ago.
"While the version of events from the trade union UNITE contains factual inaccuracies, Lidl cannot comment on details regarding individual employees particularly because the process is continuing and in light of the need to observe employment rights."
Unite says it is consulting lawyers to bring forward a potential claim against the "pay discrimination", and says it has the backing of local politicians who have agreed to write to the company’s German headquarters.
The union has also called a solidarity protest for pay equality outside Lidl on High Street, Belfast on Thursday.