AIB has insisted there were no irregularities in its deal to sell its Polish assets to Santander.
It announced last Friday that it had agreed to sell its stake in Zachodni WBK for €3.1bn.
However today Poland's financial regulator said it was investigating the deal amid concerns that confidential information may have been exchanged in advance of the agreement.
AIB said proper procedures were followed.
Finance Minister Brian Lenihan meanwhile believes the probe has been launched simply because there had been a rival state-sponsored Polish bid.
"The Polish regulator would not have a function in trying to protect the market in that way, or trying to distort the market," Minister Lenihan said.
"It was made clear to me by the Polish authorities that the question of any interference by their regulator in this was out of the question.
"Clearly AIB have established their credibility in the marketplace by receiving this bid from Santander."