The Spanish Labour Inspectorate has found Ryanair committed breaches of employment law, some of which were deemed "very serious".
The findings are contained in a 4-page judgment issued by the Labour Inspectorate revealed by the Spanish union SITCPLA.
According to SITCPLA, Ryanair was found to have obstructed the work of the inspectors in five instances, which were deemed "very serious".
In eight cases, Ryanair was found to have violated the crew's right to strike, a violation deemed "serious".
In addition, agencies from whom Ryanair sources personnel, Workforce International Contractors Ltd and Crewlink Ireland Ltd, were also found to have violated the workers' right to strike.
It’s understood that the findings relate to events surrounding union protests on 25 and 26 July, as well as on 28 September.
Staff received calls and emails asking them to confirm whether they were exercising their right to strike, and whether they would sell products on flights.
SITCPLA welcomed the findings of the Labour Inspectorate, as did fellow union USO.
As yet it is unclear what level of penalties or sanctions may be imposed on the low cost airline.
Ryanair have been contacted for a response, which is awaited.