Unionized workers at GM Korea decided to go on a partial strike after they failed to reach an agreement with the company in wage negotiations, according to the union Friday.

The union will proceed with a four-hour walkout on Friday and next Monday, it said.

GM Korea and its unionized workers held 21 rounds of negotiations beginning in July. The last one ended after 10 minutes, according to the related parties.

The partial strike is expected to weigh on GM Korea as it will deepen production losses.

GM Korea’s vehicle production from January to September decreased by 60,000 units on-year, according to the company. In addition, the company produced 1,700 fewer vehicles than usual this month as workers have refused to work overtime since Friday last week.

GM Korea said it had tried to prevent the strike as the company expects its operating losses to continue.

Local partner firms of GM Korea also released a statement expressing concern over the extended decline in production.

In the negotiations, the workers demanded an increase in their base pay of around 120,000 won ($105.7) per month. They also asked the company to increase their annual performance bonus to 6 million won plus the equivalent of 400 percent of their monthly wages.

But GM Korea refused to increase their base pay this year, saying it could raise it by 22,000 won per month starting next year.

GM Korea also offered the workers an annual performance bonus of 7 million won. The original offer from GM Korea was 5.5 million won, but the company offered an additional 1.5 million won if workers agreed to its terms and conditions.

The company also offered to raise the performance bonus by 1.3 million won next year.

By Shim Woo-hyun (ws@heraldcorp.com)