Taoiseach Bertie Ahern has said the Government had no advance warning of Aer Lingus' decision to move its Heathrow connection from Shannon to Belfast.
Speaking in Dublin tonight, Mr Ahern said the decision was "disappointing."
"They made a commercial decision for commercial reasons and that's their view and they're not open to change."
"We wish they didn't make that decision but that's what they did and that's a commercial decision whether we like it or not."
Mr Ahern said the region must now focus on filling the slots left over by the airline.
"We are not going to do anything to affect, or undermine that commercial decision. It is legally within their entitlement. We now have to try to get another operator in. Connectivity to Shannon is vital," he added.
Meanwhile, British Airways has emerged as a possible contender to replace Aer Lingus's Shannon-to-Heathrow route after an approach by the airport's chairman.
Minister for Transport Noel Dempsey said today the Shannon Airport Authority was continuing attempts to find an airline to operate flights to Heathrow, which included British Airways, after Aer Lingus decided last month to cut the route and switch to Belfast.
BA chief executive Willie Walsh, who previously headed Aer Lingus, has also confirmed Shannon airport had approached the carrier. But he said since a telephone conversation with Shannon Airport chairman Pat Shanahan more than 10 days ago there had been no formal proposal put forward.
A Shannon Airport Authority spokesman said was "very early days" and too early to predict an outcome. Talks were commercially sensitive and would take time, he said.
Previous negotiations with US carriers had taken two years to secure service.
The authority could not comment on which airlines it had approached, but it was not "rocket science", the spokesman said. "How many carriers have a presence in the Irish market place? It's not a huge number for a start."