More than 4,500 workers from Quinn Insurance are voicing their anger over the decision to place the company into administration.
They are protesting in Dublin and Cavan over fears that 5,500 jobs have been put at risk by the Financial Regulator's decision.
Some 1,500 workers turned out at the Cavan protest, with 3,000 taking part in Dublin.
Workers say the ban on the company taking on new business in the UK is particularly damaging.