Europe's biggest budget airline averted widespread strikes before last Christmas by agreeing to recognise trade unions for the first time in its 32-year history.
But the airline, which operates in 37 countries and last year carried some 130 million passengers, has since struggled to reach agreement on terms in some countries.
This has led to minor disruption in Germany and Portugal and the Irish Air Line Pilots' Association (IALPA) said it would ballot pilots if a new system for dealing with base allocations, promotions, and leave was not introduced.
IALPA began the ballot last week, a letter to members seen by Reuters on Monday showed and the results were due on Tuesday.
However, a memo circulated by IALPA later on Monday said it had extended the vote to July 3, giving pilots more time to consider "such an important matter" and avoiding a clash with a meeting of Ryanair's unions across Europe organised by the European Cockpit Association.
"It is self-evident that Ryanair and its on-going disputes with pilots across Europe will be a feature on the agenda of the ECA Conference," it said.
A spokesman for Ryanair, which this month signed its first cabin crew union recognition agreements with staff in Italy and Britain, was not immediately available for comment.
(Reporting by Conor Humphries; Editing by Alexander Smith)