Employee and employer has both rights to terminate the contract. If you have not completed your probationary period you can give even at least three (3) days to one week notice for your resignation but if you already completed your probationary period or you already completed a year of employment, you are obliged to give at least a month notice.

All reasons are accepted once an employee terminates the contract, for employers...it follows the company's policies before termination not unless you breached something, they can temrinate you even for a day.