Ryanair flies from ten airports in Sweden, including Skavsta airport, south of Stockholm, which is a major Ryanair base, as well as airports in the Gothenburg and Malmö regions.
Anders Kjellgren is the contact person for the anonymous group at the Swedish Airline Pilot Association, he tells Swedish Radio: "From a union point of view it is abominable that in 2013 you have to be anonymous, when according to Swedish law you have the right as a worker to organise yourself, to be a member of a union."
He describes the Ryanair management structure as "medieval".
"It's a tyrannical management by fear, and that's how the company is run", he told Swedish Radio. "They threaten to sack them or get rid of them, if they speak out they lose their job."
Ryanair have refused to comment on Swedish Radio's report. The company previously dismissed the group as being made up of "anonymous internet trolls".