The walkout, set to begin Thursday, could involve more than 50,000 workers and is expected to dwarf a 2024 walkout that drew about 6,000 workers at the world’s top memory chipmaker.

“Around 10pm on May 19, the labor union agreed to the mediation proposal put forward by the National Labor Relations Commission; however, management expressed its refusal,” it said in a statement, adding that it would begin striking on Thursday.

“The labour union will lawfully commence a general strike tomorrow as scheduled.”

According to the union’s lawyer, around 50,500 workers are set to walk off production lines on Thursday for 18 days over a dispute about bonus payouts.

Concerns are growing within the South Korean government that a prolonged union strike could hurt the export-driven economy, with chips making up about 35% of exports.

Samsung is a major producer of chips used in everything from artificial intelligence to consumer electronics, raising the prospect that the planned walkout could cause severe disruption and losses.

The company said this year it had begun mass production of next-generation high-bandwidth memory chips, HBM4, seen as a key component for scaling up the vast data centres needed for AI development.

Long staunchly anti-union, founder Lee Byung-chul once vowed never to allow unions “until I have dirt over my eyes”.

He died in 1987. Samsung Electronics’ first labour union was formed in the late 2010s.