If you are changing employment within Singapore and you are a:
Singapore Permanent Resident:
Your employer is not required to seek tax clearance before you move to your new employment. You have to report your annual income in the tax return. If you have not received any notification to file your return by 15 March and your income for the previous year has exceeded $22,000, you have to request for an income tax form from IRAS.
Non-Singapore Citizen:
Your employer has to seek tax clearance before you move to your new employment.
Find out about tax clearance process.