35 nurses at the Mater Hospital Dublin have been warned they may no longer be able to work in Ireland.
The affected nurses haven't received letters of support confirming that their skills are needed here.
They're still waiting for the letters because of administrative delays in the Department of Business and the Irish Naturalisation and Immigration Service.
Without the letters, the nurses won't be able to work in Irish hospitals.
The INMO represents over 1,000 nurses at the Mater and has been actively pursuing this case with the employer and the government.
The union says it wrote to the Minister for Health on December 6th, calling on him to expedite the process.
Albert Murphy Industrial Relations Officer with the Organisation, says some services at the Mater Hospital may have to be curtailed as a result.
He told Today FM "They are highly specialised nurses. They're working in the high dependency unit, they're working in theatre, they would be working in transplant programs.
"If they don't get the visas on time - these letters of course - they'll have to stop working until such a time that the bureaucracy sorts itself out. If it's not sorted out there could be a curtailment of services."