Although the strike was by pilots based in the Republic of Ireland, union leaders say it could have a knock on effect across the United Kingdom as the budget airline attempts to fill the shortage.
An empty Ryanair customer services desk is seen at Dublin airport in Dublin, Ireland September 27, 2017.
"The ITAA is calling on Ryanair and its pilots to resolve these internal issues and end this proposed strike action", he said.
Ryanair crew have warned that they too could be joining their colleagues in strike action next week after after presenting the company's CEO Michael O'Leary with a list of demands.
More than 6,000 cabin crew based in 21 countries ramped up pressure on the carrier by threatening industrial action yesterday.
"Since Ireland accounts for less than 7 percent of Ryanair flights, we expect that 93 percent of our customers will be unaffected by any strike", it said in a statement.
It's understood that both cabin and ground crew believe that not enough is being done to improve their working conditions including pay, pressurised target-based work, seniority and annual leave.
The Irish Airline Pilots' Association balloted members over a lack of an agreement on how Ryanair deals with transfers between bases.
It said the pilots backed industrial action over management's approach to transferring pilots between its European and African bases.
Ryanair has union recognition agreements with its United Kingdom, and most recently, Italy-based pilot unions.
The Irish Transport Workers Federation said that a decision on strike action would be a matter for unions in individual countries.
She said any compensation depends on when passengers are notified of a cancellation or delay and that most of the time airlines offer a re-route or a flight at a later day depending on seat availability.
Ryanair has described the demands as "pointless" and says cabin crew get sick pay, a 400-euro annual uniform allowance and could earn up to 40,000 euros a year.
"What Ryanair pilots are asking for is commonplace in many airlines and is not unreasonable".
It follows cancellations of more than 1,100 flights also in May.