The European Central Bank is increasing interest rates by a record of 0.75%, in a major blow to mortgage-holders.
The changes will take effect from next Wednesday - and follow a 0.5% increase in July.
Irish people on tracker mortgages will automatically see their payments increase.
220,000 customers on variable mortgages are also likely to be affected.
Ireland's three main banks decided not to pass the last increase on, but is likely to this time.
