It is a fairly common practice for contracts of employment to have an increasing amount of notice based on length of service. However, for probation periods it is usually one week or month.
The contract of employment should state what the notice periods are.
In general, the period of notice should be equal between the employer and employee, for example each giving the other one month’s notice. However, some employers provide unequal notice, for example the employer is required to give one week’s notice and the employee is required to give twelve weeks’ notice (although this is fairly rare).
You can find out more about probation periods here.