The country's largest labor union body urged authorities Thursday to add tougher overwork prevention measures when the government moves forward with plans to introduce a merit-based pay system for highly skilled jobs.

Based on the request by the Japanese Trade Union Confederation, known as Rengo, the government is likely to revise a deadlocked bill it has submitted to the Diet with the aim of introducing the so-called white-collar overtime exemption system.

The government insists that the system will enable certain highly skilled employees to work more flexibly. But opposition parties suggest that plan would take away overtime pay while encouraging overwork from staff who will become exempt from work-hour regulations.