HYUNDAI Motor Co workers have rejected a pay agreement reached by South Korea's biggest auto maker and its union, threatening to prolong stoppages that have cost the company more than US$400 million in lost output.

A total of 26,252 workers, or 58 percent of union members, voted against the wage deal reached on Tuesday, according to a statement posted on the union's Website.

Hyundai Motor and labor leaders agreed on a 5.6-percent basic pay increase and shorter working hours, Bloomberg News reported.

Workers have staged partial strikes on nine days since July, costing Hyundai production of 31,556 vehicles, valued at 487.7 billion won (US$436 million), according to a company estimate.

'Workers just want more money,' said Song Sang Hoon, a Seoul-based analyst at Kyobo Securities. 'There could be more production lost before they reach a deal.' He has a 'buy' rating on Hyundai.

The auto maker's third-quarter sales may be 7.2 trillion won compared with a previous estimate of 7.9 trillion won, Song said.