The law states that the company must allow each employee an unbroken two weeks off if the employee so wishes; this can include public holidays.
It is not complusory to take two weeks off in one go but if you want to, the company has to allow you to do so. Bear in mind though, you still have to agree the specific dates with the employer and you can't just demand a certain two weeks off at your own choosing e.g. if other staff are off at the same time, you probably won't get those dates off.
If the employer compells you to take two weeks off in one go, there is nothing that you can really do about it. If you are really unlucky (like me), you may be compelled to take specific dates off, which often happens in the middle of the summer which is the most expensive time of the year to go on holidays