Shares in AIB fell 49c to €21.06 following their announcement that it is putting up its interest rates.
That helped propel the ISEQ into the red by the end of day's trading, finishing down 22.45 points to 8505.37.
The other financial heavyweights did not fare much better. Irish Life and Permanent fell 11c to €19.53, Anglo Irish Bank fell 3c to €13.83 and Bank of Ireland remained unchanged at 15.85.
Elsewhere, Aer Lingus was down 1c to €2.87, while Ryanair rose 5c to €8.60.