Hyundai Motor's union struck for four hours across two shifts on Wednesday and will walk out again on Thursday and Friday, the latest turn in a labor dispute that began in the chip industry and has since spread across Korean manufacturing.

A string of strikes are scheduled to follow. Unions at carmakers Kia and Renault Korea have both cleared the legal threshold to strike after members voted in favor and the National Labor Relations Commission suspended mediation in their wage talks. Steel producer Posco goes before the same commission on Aug. 6 after collective bargaining broke down. Shipbuilders HD Hyundai Heavy Industries (HHI) and Hanwha Ocean head into the summer holiday period with wage and collective agreements unsettled.

The prospect is a chain of stoppages across the auto, shipbuilding and steel sectors, disrupting production across the industrial base.

This week's protest at Hyundai follows two earlier rounds, two hours a day from July 13 to 15 and four hours a day from July 20 to 22 for both the morning and afternoon shifts, bringing the total downtime to 36 hours across those two rounds alone. Industry estimates put the lost output at about 18.7 billion won, or $12.8 million, based on average vehicle prices and each plant's units-per-hour rate.

Manufacturing has long treated the run-up to the summer holiday in late July and early August as the effective deadline for a settlement. Unions that won the right to strike would generally sit on it and calibrate industrial action against the progress of talks, production schedules and demand, intending to mitigate lost wages and hostile coverage for unions, while management would be spared the worst of disruptions and delivery delays.

When strikes did come, they often landed in slow periods when unsold stock was piling up or during holidays when plants were running below capacity. The choreography was tight enough that both sides could absorb it, and the exercise drew comparisons to a prearranged sparring bout.

This year the calculation has changed, and part of it is legal.

The "Yellow Envelope" law, an amendment to Articles 2 and 3 of the Trade Union and Labor Relations Adjustment Act that took effect in March, bars employers from pursuing damages large enough to threaten the livelihoods of union members or the survival of a labor organization. Under the new law, the legal and financial repercussions of walking out for workers have narrowed sharply.

The rest traces to a settlement nobody expected to set a precedent. Samsung Electronics and its union fought over performance pay in May until Employment and Labor Minister Kim Young-hoon stepped in as mediator and brokered a deal to allocate a special semiconductor bonus worth 10.5 percent of an agreed business-performance measure, with no cap on the payout rate.

The agreement averted a strike. It also became the point at which unions in industries with margins nothing like the semiconductor sector's began demanding a fixed percentage of profit.

Hyundai Motor's union is asking for 30 percent of last year's net profit, while unions at Kia and HD HHI want 30 percent of last year's operating profit.

"The government stepped in and effectively institutionalized percentage-of-profit bonuses, and other unions' expectations went up a great deal as a result," a manufacturing industry source said.

The labor commission's own usefulness is now in question. The sequence has become routine: a strike ballot, an application for mediation, then a decision to suspend talks. Critics say the procedure has hardened into something closer to a licensing system for strikes.

Some labor specialists argue that framing the issue around the annual fight over pay is misguided, and that the two sides need more in-depth talks that take into consideration how their industries are changing.

"Korea has a long tendency of the government intervening in individual labor relations and controlling strikes through legal authority or tougher legislation, so a culture of the two sides bargaining autonomously and settling matters by agreement never took proper hold," Lee Jun-hee, a professor at Kwangwoon University, said.

He does not lay the blame on one side. Businesses, in his reading, have overreacted to the Samsung settlement.

"There is an element of industries reacting somewhat over-sensitively since the Samsung Electronics negotiation on operating profit-linked bonuses," Lee said.

"Advanced industrial countries all developed by accumulating this same experience of conflict and bargaining, so labor and management should be left at the table to come up with their own answers about the future."