Cabin crew at Ryanair based in Italy, Portugal, Spain and Belgium say they will strike in late July.
Cabin crew in Italy will go on strike for 24-hours on 25 July, while crew in Spain, Portugal and Belgium will strike for 48 hours on 25-26 July.
Unions said further action may follow if the Irish airline does not make concessions on some employment terms.
On Wednesday the unions issued a list of changes they wanted to their terms and conditions.
They include a request to be paid into bank accounts in their own countries, rather than in the Republic of Ireland.
Earlier this week, pilots directly employed by Ryanair and who are members of its Irish trade union said they would will go on strike for the first time on 12 July.
Last year, Ryanair pilots went on strike to protest about their working conditions.
After a long-standing hostile attitude to unions and a refusal to allow such organisations to represent staff, Ryanair finally agreed to union recognition in December.
The pilots are striking as they say conditions that prompted last year's industrial action have not improved sufficiently.
The four unions representing cabin crew said in a joint statement: "We call on the European Commission, and the governments of every European country where Ryanair operates, to act upon the social dumping performed by the Irish low cost carrier and to enforce the EU employment and national imperative legislation."
The statement was signed by Belgium's CNE/LBC, Spain's SITCPLA and USO, Portugal's SNPVAC and Italy's Ultrasporti unions.
They do not represent all Ryanair cabin crew in those countries, but have said other staff are welcome to join the action.
Ryanair has said employment conditions for its staff are competitive, if not better, than those offered by rivals.
It flies in 37 countries and carried 130 million passengers last year, making it Europe's biggest by passenger numbers.