Siptu has ruled out further negotiations with Aer Lingus management on its cost-cutting programme until they give a commitment not to introduce lower terms and conditions for new recruits.
The airline has already taken the first step in implementing its plan by issuing contracts to new cabin crew with revised terms and conditions.
The National Implementation Body (NIB) recommended on Monday that unions and Aer Lingus management hold three weeks of intensive talks at the Labour Relations Commission and the Labour Court if necessary to resolve the dispute.
A Siptu spokeswoman told ireland.comtoday that the introduction of revised terms for new recruits is "in breach of the agreement signed by management before Christmas.
"In the agreement, management agreed not to impose lower wages or conditions without negotiation", she said.
Siptu's national industrial secretary, Michael Halpenny said: "We consider this to be a breach of an existing agreement and have referred the matter to the Labour Court.
"We are willing to engage with the process recommended by the National Implementation Body but we want this issue sorted," he added.