Aer Lingus Chief Executive Christoph Mueller has said he was not aware of any legal action against the unions who are threatening to go on strike at the airline over pensions.

Reports on Friday said the airline had written to SIPTU to warn it that the company could take all steps, including legal action, to prevent industrial action.

Speaking on RTÉ's Morning Ireland, Mr Mueller said he was not aware of "speculation of that nature".

He said industrial action was not the right course of action to bring the pensions issue to a satisfactory conclusion.

Mr Mueller said a solution could only be brokered at the negotiating table.

"We have so many different parties. I have doubts about whether a parliamentary solution can be found. Even if that is not the case, a strike is not accelerating that process," he said.

Mr Mueller was speaking as the airline reported operating profit of €61.1 million for 2013.

That was in line with its stated guidance, but was lower than the €69m reported last year.