Workers in the 27-nation European Union cannot lose the right to a paid vacation just because they are ill, the European Court of Justice ruled.

Its ruling clarified the meaning of the EU labor legislation at the request of a German and a British court hearing cases of workers denied paid leave due to illness.

The EU's Working Time Directive requires governments to ensure national paid vacation rules do not end up eroding the right to paid leave, the EU court said. It said that right cannot evaporate because of illness and workers must be able to take a paid leave in another period.

The ruling immediately drew criticism. Letting workers accrue paid vacation benefits while on sick leave "will have serious and practical" problems for employers, said Tim Marshall, a partner and head of employment at DLA Piper LLP in London, one of the world's largest law firms, which represents many multinational corporations.

"In these difficult times further constraints could prove too much for some employers," he added.