Can an employee be ordered to take vacation days?

A holiday period may be moved to another time when there are special reasons for doing so.
Special reasons in accordance with section 12 of the Annual Holidays Act may be that important social functions must be maintained. An example of such a function is healthcare. It may also be the case that safety at the workplace cannot be maintained if staffing levels are too low. Special reasons should be foreseen.
You have the right to save five vacation days per year under the Vacation Act, i.e. the difference between 20 and 25. After that, the provisions of the agreement come into force for vacation days in excess of 25. If the employer and employee do not reach such an agreement as you mention, the vacation days in question are scheduled in consultation just like any other vacation. It is the employer's prerogative to grant holidays, but there is a difference between that and specifically ordering the allocation of holidays.

In short, it can be summarized that the employer has the possibility to refuse, move and change holidays within a given framework but that their possibilities to order the taking of holidays are small. The exception is if the employee has saved more vacation days than allowed by law, contract or agreement, but the main rule is that even in these cases the vacation should be scheduled in consultation as far as possible.