A memo to workers offers an insight into the bank's fears ahead of the vote
AIB was warned its workers to prepare for a period of intense volatility following the UK's vote on EU membership.
The Irish Times has seen a memo sent to staff by its chairman Richard Pym warning of the profound economic effect that the referendum will have in both the UK and Ireland.
He warned that it is not possible to predict how Britons will vote and that, "As a bank we consider economic risk and the risks arising from a Brexit are extremely high."
"Financial markets react badly to uncertainty and businesses and households hold back on investment. It is widely anticipated that sterling will fall and UK policymakers will have a difficult set of issues to address," he said.
The letter adds that the bank's board strongly supports the UK remaining in the EU.
"As an example of just one of many problems to be overcome, the UK has not negotiated a trade agreement since accession in 1973 and it has been estimated will need to hire 500 lawyers to join the civil service to form the basis of the British negotiating team," the chairman continued, adding, "The negotiations could take a decade to conclude."
Given the volatility that the vote will create on currency markets, its exchange department will be manned for 24 hours during the vote and count.
Senior members of staff in other departments will work late into the night on Thursday as the bank reacts to the vote.