A strike at Ireland’s main airports and at Aer Lingus during St. Patrick’s weekend is now likely due to an ongoing pensions dispute.

The unions met over the weekend to talk about an €800 million ($1.1 bn) hole in the Irish Airlines Superannuation Scheme, which involves over 4,270 Aer Lingus, Dublin Airport Authority (DAA) and Shannon Airport staff, most of them represented by the trade union SIPTU.

SIPTU’s Pension Advisory Committee head Dermot O’Loughlin said on Monday it was likely the strike would take place from March 13, at the start of the weekend before St Patrick’s Day on the 17th.

Last year, Aer Lingus agreed to a Labour Court recommendation to inject a total of €140 million into a new defined contribution scheme for its staff members.  The DAA also agreed to stump up €60 million for a new separate defined contribution scheme in respect of its workers.

Unions have claimed the amounts being offered aren’t enough. Just days ago, Aer Lingus restated that its proposed €140 million lump sum contribution for a new scheme remains sufficient.

Irish Congress of Trade Unions industrial officer Liam Berney has said that unless both companies agree to put in more money, then the prospect of industrial action remained real.

Aer Lingus CEO Christoph Mueller said he believes striking will do nothing to help settle the dispute.

Mueller said he was not aware of any legal action against the unions who are threatening to go on strike over pensions. He believed a solution could only be brokered at the negotiating table.

Earlier this week, Aer Lingus reported an operating profit of €61.1million for 2013. That’s in line with its stated guidance, but down 11.6 percent from the €69 million reported in 2012.

Long haul routes performed especially well last year, with revenue up over 11 percent and passenger numbers up over 12 percent.

But short haul revenue was down 3.3 percent due to the good weather in Ireland and Northern Europe last summer as well as more competitive pricing.