Struggling chipmaker Renesas Electronics Corp., seeking to accelerate restructuring efforts, plans to slash another 5,400 domestic employees, or around 20 percent of its workforce, by the end of March 2016 through early retirements, according to company sources.

The labor union, however, opposes the plan. The move by the labor side could make it difficult for the company to carry out the personnel cuts.

Renesas aims to achieve an operating margin of 10 percent in fiscal 2016. It cut about 3,000 employees last fall after the third round of calls for early retirement, but it has been forced to consider additional restructuring measures as it fell short of its goal.