SEOUL (Reuters) - A workers' union at Samsung Electronics ( SSNLF ) in South Korea is set to stage a three-day strike from Monday and has warned it could take further action against the country's most powerful conglomerate at a later date.

The National Samsung Electronics Union (NSEU), whose roughly 28,000 members make up over a fifth of the firm's workforce in South Korea, is demanding the company improve its performance-based bonus system and give workers an extra day of annual leave.

It is not immediately clear how many workers will join the strike, but the union's poll found about 8,100 members saying they would do so as of Monday morning.

Lee Hyun-kuk, a senior union leader, said in a YouTube broadcast last week that another round of strikes could occur once the three-day stoppage is over if the workers' demands are not heard.

The union plans to hold a rally on Monday morning near Samsung's headquarters in Hwaseong, south of Seoul.

Analysts, however, say the strike is unlikely to have a major impact on chip output as most production at the world's biggest memory chipmaker is automated.

Last month, the union staged a walkout by using annual leave, its first such industrial action, but the company at the time said there was no impact on production or business activity.

Though it will have little impact on output, the labour movement shows decreased staff loyalty at one of the world's top chipmakers and smartphone manufacturers, analysts say, adding another problem for Samsung as it navigates cutthroat competition in chips used for artificial intelligence applications.

Samsung estimated on Friday a more than 15-fold rise in its second-quarter operating profit, as rebounding semiconductor prices driven by the AI boom lifted earnings from a low base a year ago, but its share price performance has been lagging behind South Korean chip rival SK Hynix.