Leaders of a South Korean union representing tens of thousands of workers at Samsung Electronics staged a protest on 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), said.

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

Union executives gathered on Thursday outside Samsung Chairman Lee Jae-yong’s house, holding pickets that read “Samsung Electronics’ strike, Lee Jae-yong should be accountable”.

Another displayed a picture of Lee holding a finger to his mouth with the caption, “Shh! Labour union, what’s that? Samsung strike, what’s that?”

A handful of police were deployed at the premises and the protest was interrupted by the police warning the union they were not allowed to chant.

“In the 25 days since the strike began, all Lee has done is attend the wedding of the son of Asia’s richest man and give out Samsung phones to Olympic athletes that are worth over 30bn won ($22mn),” union member Kim Jae-won told reporters.

Lee was a guest at the wedding of Indian billionaire Mukesh Ambani’s youngest son Anant in July.

Last week he attended a banquet co-hosted by French President Emmanuel Macron and International Olympic Committee President Thomas Bach at the Louvre Museum.

The union claimed that the company was trying to break the strike with illegal means, including creating a “blacklist” of strike participants.

“We will publicise all of this,” Son Woo-mok, head of NSEU, said.

“Labour suppression, unfair labour practices, industrial accidents, the list continues.”

Samsung said on Wednesday it was “communicating and discussing to ensure that this labour union strike ends early”, adding there was “no problem with responding to our customer volume”.

The first labour union at Samsung Electronics was formed in the late 2010s.

The National Samsung Electronics Union, which has around 36,000 members, or nearly a quarter of the company’s total workforce, claims labour organising remains taboo at the company. Two years ago, the union staged a demonstration in front of Lee’s residence, successfully securing three additional holidays.

In 2020, former Samsung employees faced criticism for their unorthodox protest methods, which included drinking and strumming guitars outside Lee’s home.