Location is in Europe. In my country there is a legal 1 month requirement for giving notice for employees on a permanent contract. I can understand that, it takes time to launch the job posting, interview and then hire and train the employee. 1 month is plenty.
But for my company, it has to be 3. Why? I don't know, it just says it is 3. Unless you can come to an agreement with your manager. Sometimes I wonder if telling them 'I won't show up after X date' is sufficient to get their 'agreement'.