The top court has ruled in favor of workers at Hyundai Heavy Industries, ending a nine-year battle between the union and the company over periodic incentives.

The Supreme Court on Thursday overturned a lower court ruling in favor of the management, sending the case back to the Busan High Court for a retrial.

The nine-year battle was focused on whether regular incentives must be paid as part of base salary and severance pay. 

Hyundai Heavy workers demanded the company recognize the incentives as part of their base salary, and asked for the overdue amount of incentives that resulted from an accounting error. The incentives in arrears are estimated at around 600 billion won.

The Supreme Court made clear that non-periodic incentives must also be recognized as base salary.

It also said that it's unfair to reject workers' demand for regular incentives even when a company is undergoing financial trouble, as external factors and economic volatility can be hedged in advance.