Hi, Strictly speaking, whatever terms and conditions are mutually agreed upon between the employer and employee at the time of joining will bind the employee. You cannot force the employee to accept unrealistic interim amendments in employment terms. The right process is to make it applicable to future new joiners and not the existing employees.
If an employee fails to accept the revised terms, it is better to collect their resignation rather than using the termination option. You cannot terminate the employee on the above grounds either.