In:
As an employer, you are required to seek tax clearance (IR21) when any of your non-Singapore Citizen employees such as Permanent Residents (PR), etc cease employment with you in Singapore.
However for SPR, you may wish to get the self-declaration that he/she is not leaving Singapore permanently when he/she is ceasing the employment based on the nature of his/her immigration status.
You have the responsibility to file the Form IR21 and withhold all monies due to the employee for tax clearance purpose.