Pilot union BALPA is conducting a survey to gauge the support of Ryanair's UK-based flightcrew for legal or strike action over working practices.
The union says the survey is a response to "growing dissatisfaction with the company".
One of the questions BALPA asks is whether pilots would be "prepared to support industrial action to achieve their objectives"; another, whether staff hired on agency contracts would support "a group legal action to establish employee or worker rights".
BALPA general secretary Brian Strutton argues that Ryanair is "unique in the complexity of its employment structures", and says the survey is partly aimed at finding out whether pilots want the union to "test the legality" of the airline's practice of using third-party contractors to hire flightcrew.
"We will be guided by the Ryanair pilots in all of this work," he adds.
Ryanair does not recognise union representation in its dealings with pilots, preferring to negotiate with them through employee representative committees (ERCs) at each of its bases. The airline regularly uses recruitment agencies such as Crewlink to hire pilots.
Responding to BALPA's statement, Ryanair says a majority of its pilots are direct employees, adding: "A minority are contractors, just like the contractor pilots which predominate among Norwegian, Wizz, EasyJet and other low-cost airlines in Europe, and the many contractors employed by hospitals, hotels, airports and media companies".
On this basis, the airline argues, "BALPA's claims about Ryanair's 'complex employment structures' are false".
Pilots who wish to discuss or improve their pay or conditions "can do so at any time using the established collective bargaining (base ERC) process", states Ryanair.