Minister for Transport Leo Varadkar has said the decision by Aer Lingus to sue SIPTU for damages incurred due to threatened industrial action is "unhelpful."

Mr Varadkar said all parties should be "focusing on the core problems so that the public won't be inconvenienced by future strikes, and so that members of the pension scheme can get clarity regarding their future entitlements."

Today's planned four-hour strike was blocked on Wednesday when the High Court issued an injunction to the Dublin Airport Authority restraining SIPTU from carrying out the stoppage.

In proceedings issued today, Aer Lingus is seeking damages under a number of headings, including breach of contract and conspiracy.

It also claims that SIPTU has unlawfully interfered with the airline's trade or business.

The plenary summons claims that SIPTU induced a breach of Aer Lingus contracts with its customers.

The company is also seeking damages for loss and damage, which it said was inflicted by unlawful means.

SIPTU said it will "vigorously resist" the legal proceedings.

A spokesperson said the union will be consulting with its legal advisors over the next number of days.

Aviation sources have estimated the potential cost to Aer Lingus at multiple millions of euro even though the strike was called off 36 hours before it was due to proceed.

The airline is seeking a declaration from the courts that the secret ballot held by SIPTU ahead of the threatened strike was unlawful.

It wants a declaration that no valid trade dispute exists between Aer Lingus and SIPTU in accordance with industrial relations law, and that the industrial action was not in contemplation or furtherance of any such trade dispute.

It alleges that SIPTU has failed to comply with a collective agreement and failed to exhaust procedures provided for in that agreement.

The legal documents were served on the union this morning.

Ryanair has said it was reviewing its options.

Aer Lingus has told SIPTU's Pensions Policy Advisor Dermot O'Loughlin that it is holding him personally and SIPTU fully responsible and liable for loss and damages it sustained.

In a letter to Mr O'Loughlin, Aer Lingus Director of Change and Engagement Sean Murphy said the union's notification that the strike would not be going ahead was "too little too late".

Mr Murphy said Mr O'Loughlin will be fully aware that Aer Lingus has already suffered significant loss and damage as a direct consequence of what he describes as the "unlawful" action.

He said Aer Lingus has had to endure significant adverse effects on its forward booking profile, reorganise its flights schedule, cancel flights, re-book passengers and hire in additional aircraft.

Mr Murphy stated that Mr O'Loughlin would be aware from correspondence that the purported industrial action was "unlawful", and would lead to loss and damage to Aer Lingus.

He also noted that Aer Lingus "called on you not to proceed with the industrial action".

Mr Murphy concluded by saying that in all the circumstances, the airline has issued proceedings against Mr O'Loughlin and SIPTU holding them fully responsible and liable for all the resulting loss and damages sustained.

He also stated that the airline reserves the right to take any additional necessary action, including court action, to prevent any further loss and damage.