SEOUL, Jan 12 Unionised workers at Hyundai Motor Co. 005380.KS, South Korea's top

SEOUL, Jan 12 (Reuters) Unionised workers at Hyundai Motor Co. , South Korea's top auto maker, said on Friday they will launch a strike amid a bonus dispute.

But the union had not decided the timing and the degree of the labour action, Song Hi-sok, a union spokesman said.

''The action is a kind of extension of 2006 wage negotiations,'' Song told Reuters by telephone.

The decision by union representatives comes as Hyundai aims to more than double global revenue growth in 2007, which some analysts see as too aggressive amid sluggish local sales.

Unionised workers at Hyundai have declined overtime since late December, demanding a 2006 bonus equivalent to 150 percent of one month's salary. They received only a month's salary as bonus after Hyundai said yearly output targets were not met.

Hyundai said the refusal of extra work has cost the company 12,798 vehicles or 190.1 billion won ($202.2 million) in lost output.

The company on Monday filed a lawsuit against 26 union officials, seeking 1 billion won compensation.

Poor labour relations are seen as a major hurdle to Hyundai's target of becoming the world's No.5 automaker by sales volume along with its affiliate Kia Motors Corp. , up from the current No. 6.

Union members staged strikes on a total of 33 days in 2006, asking for higher wages and better working conditions. Some of the protests were made in opposition to new labour laws and the current free trade agreement talks with the United States.

Hyundai Motor shares were flat at to 63,900 won by 0413 GMT, compared with the wider market's <.ks11> 1.51 percent gain.

($1=940.0 Won) REUTERS CS DB1144