Workers living in Northern Ireland who have received the new Covid-19 Pandemic Unemployment Payment have been asked by the Department of Employment Affairs and Social Protection to return the money.
The €350 a week social welfare payment is only available to laid-off employees and self-employed workers who are resident in the State.
However, RTÉ's Morning Ireland programme understands some applicants who work in the Republic but live in Northern Ireland have been given the payment.
An office worker, living in Co Armagh but working for 15 years in Co Monaghan, told the programme she was unaware of the restrictions when she filled out the online application.
"I didn't know you had to be a resident of the Republic and I put in my address in Northern Ireland," she said. "The payment came through but I'm afraid to spend a penny of it. I'm anxious and stressed."
She described feeling let down by the welfare system.
"Everybody should be pulling together but that doesn't seem to be the case," she added. "The Revenue doesn't seem to mind where my address is when I am paying tax."
The department said it had received unprecedented numbers of applications over the last number of weeks and it was working through checks on these once they are processed.
"If a person has received any payment to which they were not entitled, they should refund this either directly to the department's bank account or they can do so by debit card," it said in a statement.
"Where a person thinks they inadvertently applied for the payment, they must close their application and we would kindly ask them to do so now."
Border workers are advised that they must claim unemployment benefits where they live, not where they work.
However, there is not an equivalent, universal Covid-19 payment in Northern Ireland and basic unemployment rates are between €65 and €80 per week.
Substitute primary school teacher Ronan Gregory said the difference in available benefits was leaving a "sour taste".
The 26 year-old lives in Co Armagh and was teaching in Co Monaghan and Co Louth.
"I just assumed because I was paying my tax in the south, I thought they would support me," he said.
"I suppose it's alright for the other teachers in the school because most of them are full-time. They are secure, but I wasn't. I have nothing for the foreseeable coming in. It's crazy."
The department said Northern Ireland-based workers were entitled to the temporary wage subsidy scheme in which the State subsidises wages by up to 70%.
However, employers must have sufficient cash flow to pay the remainder of the salary.