Unionised workers at Hyundai Motor plan partial strikes starting Friday and a full one-day walkout on Tuesday to demand higher wages and bonus payments, a union official reportedly said.

Reuters noted that South Korea faces a tough bargaining season with unions every summer, but labour unrest this year poses a big headache for a government struggling to bolster depressed local consumption and lift business investment to guide growth higher.

Hyundai’s strike is also widely expected to spark similar industrial action by affiliate Kia Motors, SUV maker Ssangyong Motor and GM Daewoo Auto & Technology Co., the news agency added.

According to Reuters, workers belonging to Hyundai’s 40,000-strong union, which demanded a 10.48% increase in base salary and bonus payout equivalent to 30% of the firm’s net profit, will down tools for three hours on Friday and for six hours on Monday.

They also plan a full strike on Tuesday, the union reportedly said – about 70% of unionised workers voted in favour of the strike.

The news agency noted that Hyundai’s union is the country’s largest and most powerful member of the umbrella labour group Korean Confederation of Trade Unions, which is planning a general strike among hospital workers, taxi drivers and some other industry unions.

“We did not have another choice but to go on strike as the management has not shown a sincere attitude towards negotiation,” union spokesman Chang Gyu-ho told Reuters.

“Whether to stage further strikes after Tuesday wholly depends on what the management does at the negotiating table,” Cho reportedly said.

Union officials reportedly said workers at Kia Motors and Ssangyong Motors are scheduled to vote on Friday whether to down tools to demand better pay and working conditions.

Analysts told Reuters Hyundai would have to overcome unruly unions and spend more on R&D if it is to emulate the success of Toyota, which has become the world’s most valuable and profitable car maker.

Hyundai wants to become one of the world’s top five car makers by 2010. It ranks seventh, selling three million vehicles last year, the report added.