The government agreed on Tuesday to sell its 25% stake in the airline to IAG, the owner of British Airways.
Taoiseach Enda Kenny said the takeover offer would be best for the Irish tourism industry and the Irish economy.
But the government has been accused by opposition leaders of trying to "ram" through the sale.
The deal will require approval by the Irish parliament, with a vote due to take place on Thursday.
Fianna Fáil's Micheál Martin, the leader of the opposition, said in a debate in the Dáil [the Irish parliament] on Wednesday that he "objected in the strongest possible manner" to the government's actions over the sale.
He said the issue should be referred to the transport committee, where witnesses should be called.
Paschal Donohoe, the minister for transport, told the Dáil the sale was a "landmark decision" and was the right one "in the interests of the country and the company".
He said the airline's head office would remain in Ireland and outlined reasons why the government believed the sale was the correct move.
He said it would strengthen the competitiveness of Aer Lingus, and would give "greater certainty to connectivity" between Ireland and Heathrow airport in London.
He added that it would bring growth to Irish airports and create employment.
Meanwhile, IAG's chief executive Willie Walsh said he understood Ireland's protection of Aer Lingus, but a deal would be a "growth story" for the airline.
Mr Walsh said Aer Lingus would "remain an Irish airline" and added that he was confident that the airline's shareholders would accept IAG's bid.
While the Irish government supports the takeover offer, Ryanair, the other big Aer Lingus shareholder, is yet to make a decision.
Ryanair chief executive Michael O'Leary recently said his company would consider any offer from IAG.
The Irish government got the best deal for the country in agreeing the sale of its stake in Aer Lingus, the Taoiseach [Irish Prime Minister] has said.