Dear Mr. Lakshmi Gopal,
Since I am not from the HR Department, my opinion may not suit you. I have heard that in corporate culture, even asking for human rights is sometimes seen as an offense by management.
In your case, you have taken two actions simultaneously, whereas both actions have different purposes.
Increment Based on Performance
It is always right that increments are given based on the last year's performance of employees. Therefore, it is true that any increment given is a reward for the work already performed by the employee.
Notice Period Increase as a Management Requirement
On the other hand, the increase in the notice period is a requirement of management and does not concern the increment.
Management should inform their difficulties and requirements and convince all the key persons individually to get better results. A sympathetic attitude should be maintained from both sides.
It seems like a judgment that employees who are willing to accept an increase in the notice period will only be given an increment. Otherwise, no employee is eligible for an increment.
If the purpose of motivation and fulfilling the requirements of employees before they complain or ask for them is not given preference by HR, employees will never look back when they get an opportunity.
Therefore, you should convince each employee separately for the increase in the notice period and not link it with the performance of employees.
Thanks / Regards
ANIL