Workers at South Korean tech giant Samsung began a three-day general strike Monday, the head of a union representing tens of thousands of employees told AFP, after talks with management broke down.

"The strike has started from today," Son Woo-mok, head of the National Samsung Electronics Union, told AFP, adding that a major rally was scheduled later in the day.

The union, which has around 28,000 members, or more than a fifth of the company's total workforce, announced the three-day general strike last week, saying it was a last resort after talks broke down.

The move follows a one-day walkout in June, the first such collective action at the company, which went decades without unionisation.

Management at the firm, the world's biggest producer of memory chips, has been locked in negotiations with the union over wages and benefits since January but the two sides have failed to narrow their differences.

"We are now at critical crossroads," the union said in an appeal sent out to members last week, urging them to support the "critical" strike.

"This strike is the last card we can use," the union said, saying that workers at the company needed to "act as one".

"This strike is not just about improving working conditions, it is about taking back our rights that have been ignored so far," it added.

Workers have rejected the offer of a 5.1 percent pay hike, with the union having previously outlined demands including improvements to annual leave and transparent performance-based bonuses.

Samsung declined a request for comment.

Samsung Electronics avoided its employees unionising for almost 50 years -- sometimes adopting ferocious tactics, according to critics -- while rising to become the world's largest smartphone and semiconductor manufacturer.

Company founder Lee Byung-chul, who died in 1987, was adamantly opposed to unions, saying he would never allow them "until I have dirt over my eyes".

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

The firm is the flagship subsidiary of South Korean giant Samsung Group, by far the largest of the family-controlled conglomerates that dominate business in Asia's fourth-largest economy.

It is world's largest memory chip maker, and accounts for a significant chunk of global output of the high-end chips.

Samsung recently predicted a 15-fold increase in its on-year second quarter operating profits, thanks to growing demand for generative AI.

Semiconductors are the lifeblood of the global economy, used in everything from kitchen appliances and mobile phones to cars and weapons.

And demand for the advanced chips that power AI systems has skyrocketed thanks to the success of ChatGPT and other generative AI products.

Semiconductors are South Korea's leading export and hit US$11.7 billion in March, their highest level in almost two years, accounting for a fifth of South Korea's total exports, according to figures released by the trade ministry. (AFP)