You may want to consult legal advice that's familiar with your local labor laws.
I assume the company proposes a change to the existing contracts. In this case you have two choices: you sign or you don't.
If you don't the company can decide what to do: Push back, accept it, fire you, etc. Ultimately what they will do depends on the reasons why the want the new policy and how strongly they feel about. So your first order of business should be to find out what's really going on, ideally through someone in management or HR that you trust.
It may also be useful to figure out, how other people in the company feel about this. If a large number of employees complain or refuse to sign this, there is little the company can do.
Even if you sign it, you should try to find out what the consequences of a violation are. Let's say you walk after 4 weeks. What would they do? Just stop paying you, give a bad reference, hit you with a massive libel lawsuit, etc. ?
Most of this information you need to find out yourself through talking to other people inside your company and consulting local labor law experts. You should do as much research as possible before engaging.
The actual engagement can be straight forward and polite. For example
"I understand that the company wants a significant change to the
existing employment contract. That's pretty unusual, so could you
please explain to me what the rationale behind this is and why you
feel that the existing provisions are insufficient?"
"I understand that the company wants to change my existing employment
contract. Personally I feel very happy with my existing contract and I
would be more comfortable leaving it the way it is. This would much
more in line with the current laws and local customs in this area. How
can we achieve this?"
See also What happens if I don't sign an updated "Employee Handbook" agreement/contract?