Administrators appointed to Quinn Insurance have warned of job cuts, the embattled company revealed.
The multinational got the go-ahead to reopen part of its UK insurance business on Wednesday night.
But the company said the administrators claimed staff were unlikely to stay at the current level given the reduction in the UK business.
They also highlighted the possible impact of administration on trading in the Irish Republic.
A statement said: "The administrators said that they welcomed yesterday's decision by the Financial Regulator.
"However, they said that the UK business will be significantly reduced compared to the levels prior to administration, and that it was likely that customers' understanding of the administration process would impact some of the company's ROI business lines.
"As a result, and regrettably, staff levels are unlikely to continue as is."
A spokeswoman for the employees urged Ireland's Financial Regulator Matthew Elderfield to reopen other segments of the UK business, warning 1500 jobs were on the line.
"This news clearly signifies the start of the redundancy process," she said. "This is a devastating blow to employees who have tirelessly been campaigning for the reopening of NI/UK business so that staffing levels could be maintained."
It is understood the assessment by the administrators will be completed by April 30 and staff notified.