Liberty Insurance is to shed 285 jobs at offices on both sides of the border.
The company, formerly Quinn Insurance, expects to cut 140 positions in Dublin, 75 in Cavan, and 70 in Enniskillen.
There are currently around 500 employees in each of the affected offices.
Patrick O'Brien, chief executive of Liberty Insurance, said the redundancies were necessary a year after acquiring the business to protect the remaining 1,100 jobs.
"We are fully committed to the Irish business, will continue to invest in our business, and believe that our arrival has been positive for the Irish insurance market and consumers," he said.
Staff were informed of the developments today ahead of a 30-day consultation period.