From 1 January 2012 employees must use their lawful holidays within 6 months after the end of the calendar year. Before 1 January 2012 holidays only declined after a period of 5 years. So the employee will have less time to use his remaining holidays after the calendar year has ended.
The change is necessary looking at the negative consequences delaying a holiday can have for health and safety of the employee.
The period of 6 months is not applicable if the employee was not able to take a holiday on time due to a qualified reason. For example a medical reason, because of a re-integration project or due to actions of the employer. Employers and employees can decide together in a central agreement to increase this period.
The change is only applicable to the lawful holidays which the employees build up from 1 January 2012, so already existing holidays will fall under the "old" rules.
What are the lawful holidays? This is calcultated as follows: 4 times the number of workdays per week. So if the employee is working fulltime the lawful holidays are 20.
Holidays received above the lawful holidays do not fall under the change. These can still be used during a period of 5 years.