Yes, reaffirmed the ECJ in Sobczyszyn v Skola Podstawowa w Rzeplinie, in a case which doesn't really say anything new.
Ms Sobczyszyn, a teacher, took convalescence leave provided by a Teachers' Charter and was unable to use her annual leave. The school said that leave had been used during convalescence. A reference was made to the ECJ on the compatibility of the domestic Polish Teachers' Charter with the Working Time Directive 2003/88/EC.
Article 7(1) provides four weeks' annual leave for every worker which is a fundamental tenet of EU social law. Only on termination can payment be made in lieu. Annual leave accrues during sick leave, Stringer. If scheduled leave coincides with sickness, a worker can designate a different time to take leave, Pereda. The purpose of paid leave is rest and relaxation. Sick leave is for recovery from illness, it is not rest; annual leave can be rescheduled on recovery, ANGED.
Whether leave has been scheduled or booked makes no difference: if sickness prevents annual leave, workers must be able to use annual leave at a later date.