Leaders of a South Korean union representing tens of thousands of workers at Samsung Electronics staged a protest Thursday outside the house of the company's chairman and heir, after fresh negotiations failed.

Thousands of union members stopped working on July 8 for what was initially meant to be a three-day strike, part of a long-running battle over pay and benefits. The union subsequently extended the work stoppage "indefinitely".

It is unclear exactly how many workers have downed tools, and Samsung has said the action is not affecting production, posting record growth and profits earlier this week for the second quarter.

"If a delay occurs in semiconductor processing, the effects won't be immediate. It takes weeks or months," Lee Hyun-kuk, vice president of the National Samsung Electronics Union (NSEU), told AFP.

The union engaged in eleventh-hour talks with management for three days, until Wednesday, but has failed to reach an agreement.

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