Some 450,000 workers will now get more protection by a key piece of labour law that spells out minimum employment standards that firms must follow.

This includes 150,000 rank-and-file workers earning between $2,000 and $2,500 each month, and 300,000 professionals, managers and executives (PMEs) earning below $4,500 each month.

These follow amendments to the Employment Act passed in Parliament on Tuesday.

Bosses will now be required by law to pay workers' salaries on time, and employees cannot be short-changed on benefits such as paid sick leave or be sacked unfairly.

Previously, the Act only covered some 1.6 million workers earning below $2,000 each month, or manual workers earning up to $4,500 each month. PMEs only get some limited protection, including help on salary disputes.

The latest changes will "ensure reasonable labour standards for workers while balancing employers need to stay competitive," said Acting Manpower Minister Tan Chuan-Jin.

They were triggered by the changing profile of the workforce with growing ranks of PMEs and changes in employment practices, he added.