Several European unions took the decision to go on strike at a meeting earlier this week in Brussels to force the airline to apply national labour laws rather than Irish law.
The European unions had said 20 June was the deadline for the low-cost airline to answer their demands, but Bruno Fialho from SNPVAC said their demands had not been met.
Ryanair continues to impose rules that are contrary to Portuguese law, he said, adding that Ryanair has to obey Portuguese sovereignty as well as Spanish or Belgian sovereignty in those countries.
When he was asked if the Portuguese cabin crews might be substituted by other nationalities as happened during the last strike at Easter, he said that would be impossible.
“As there are five European countries going on strike at the same time, strikers will not be able to be replaced as they cannot go and get them from anywhere else, he said.