This press release from Republican Sinn Féin is a little short on the necessary background detail for a full assessment of what they claim:
..anyone born in the Six Occupied Counties of Ireland has their nationality registered with the 26-County Department of Social and Family Affairs as Northern Irish.
If true it would seem unconstitutional (Though RSF wouldnt recognise that Constitution – pdf):
It is the entitlement and birthright of every person born in the island of Ireland, which includes its islands and seas, to be part of the Irish Nation. That is also the entitlement of all persons otherwise qualified in accordance with law to be citizens of Ireland. Furthermore, the Irish nation cherishes its special affinity with people of Irish ancestry living abroad who share its cultural identity and heritage.
Interestingly they also claim the Northerner who raised this was..
was asked to produce his passport to verify his citizenship!
Has holding a passport become a qualifier of citizenship for Irish people born in ‘Northern Ireland’?