Those unions have been holding meetings with Ryanair bigwigs since that announcement.
Pilots in Ryanair's home country Ireland on Thursday announced two more one-day strikes, increasing pressure on Europe's largest low-priced carrier to improve conditions to stave off a wave of industrial action across Europe.
The airline told Spanish news agency Efe that it expected to cancel about 30 of the 290 flights it had programmed.
Ryanair ended a 32-year ban the airline had held on unions in December and are already in dispute with the Forsa union.
The airline has said only Ireland-UK flights are affected.
Earlier in the week the airline said it had planned for the strike by trying to "minimise the impact" on "families travelling on holidays to Portugal, France, Spain, Italy and Greece".
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"The union and management found some common ground in talks yesterday (Wednesday) on the proposal that a joint working group could help the parties agree on a fair and transparent method to govern base transfer arrangements and related matters, but failed to reach agreement on the terms of reference for such a group".
"All customers on these flights have received text and email notification of these cancellations earlier today and our Customer Service teams are assisting them with refunds, free transfers to alternative flights on Thurs, or Wed, Fri and Saturday".
"We will contact customers in due course when we receive details".
The airline has said it "cannot rule out further disruptions in July and August".
The Irish pilots are striking over pay, working conditions, promotions and annual leave in the second burst of union action against Ryanair since the airline chose to recognise trade unions in December.
The announcement came hours after Ryanair said that Thursday's strike by some of its pilots had got them nowhere and if they insisted on further strikes then so be it.