South Korean truckers have embarked on aggressive strike action, threatening to severely curtail shipments of raw materials for semiconductors and petrochemical products.
The move comes on top of action at steelmaking giant POSCO and carmakers Hyundai and Kia.
The strike led to a halving of production at Hyundai's biggest factory complex in the industrial hub of Ulsan on Thursday, with upto 1000 truckers protesting in front of the complex on Friday according to witnesses.
"There are some disruptions to our production due to the truckers strike. We hope production will be normalised as soon as possible," a Hyundai official said.
Hyundai normally makes about 6000 vehicles a day at its plants in Ulsan, including the high-margin Genesis SUV and Ioniq 5 electric vehicle.
Entering its fourth day, the strike has disrupted shipments for a wide range of companies and is slowing activity at ports.
The movement of containers at Ulsan port, which accounts for about 10 per cent of South Korea's port traffic, has been suspended since June 7, a government official said.
About 7500 members, or 35 per cent, of the Cargo Truckers Solidarity Union, are expected to strike on Friday, according to South Korea's transport ministry.
The government estimates about six per cent of the country's 420,000 truck drivers belong to a union.
Kim Gyeong-dong, a trucker union official, said the union ran out of funds to finance the strike on Thursday and it was unlikely action could last another 10 days.
South Korea is a major supplier of semiconductors, smartphones, cars, battery and electronics goods, and the latest industrial action further raises uncertainty over global supply chains already disrupted by China's strict COVID-19 restrictions and Russia's invasion of Ukraine.
The truckers plan to stop shipments of raw materials for semiconductors produced in Ulsan, Park Jeong-tae, a senior truckers union official, said.
Samsung and SK Hynix, two of the world's biggest memory chip makers, declined to comment.
Park added the number of vehicles entering an Ulsan petrochemical complex has been cut to one tenth of normal levels and truckers would be telling non-union drivers not to enter the complex.
South Korean President Yoon Suk-yeol, in power for a month, said on Friday the government planned to take a neutral stance in the dispute.
Police said around 30 union members have been arrested so far and it will respond strictly to illegal acts at strike sites.
The truckers, regarded as self-employed contractors in South Korea, are seeking pay increases and a pledge that an emergency measure guaranteeing freight rates would be extended.
The measure was introduced during the height of the COVID-19 pandemic and is due to expire in December.
The drivers also want freight rates to apply to a wider range of trucks, not just container trucks and cement trucks.