Investigators on Thursday raided the offices of Samsung Electronics after summoning the head of its parent group a second time for questioning as part of a probe into an alleged bribery slush fund.
Samsung Electronics, the world's largest computer chip maker, confirmed that investigators were searching its headquarters in central Seoul.
The raid came after group chairman Lee Kun-Hee, 66, was asked to appear at 2:00 pm (0500 GMT) on Friday. He was questioned first time last week during the inquiry, launched by a team of special prosecutors in January.
"Chairman Lee has been asked to appear for questioning tomorrow," Yun Jung-Sok, a spokesman for the investigators told reporters.
When he appeared for questioning last week, Lee flatly rejected allegations that his group had raised millions of dollars for a bribery slush fund. He also denied he had illegally helped transfer control of the group to his son Lee Jae-Yong.
But Lee senior apologised after undergoing an 11-hour interrogation, saying he would do his best "not to let this kind of thing happen again."
"I will humbly accept the results of the special probe and do my best not to let this kind of thing happen again."
Parliament voted to set up the independent probe into claims by the group's former chief lawyer that it had created a slush fund totalling 200 billion won (197 million dollars) to bribe government officials and politicians.
The special prosecutors have also investigated whether control of the group was illegally transferred from Lee to his son, who is a senior executive of Samsung Electronics.
The son was questioned in March but investigators said there was insufficient evidence to indict him.
Lee's wife Hong Ra-Hee, who runs a prestigious art gallery, was questioned last week over claims that the suspected fund was used to buy expensive paintings.
Lee and other corporate leaders were questioned in 1995 over suspicions that they bribed politicians.
Lee was later convicted of contributing to a slush fund for then-President Roh Tae-Woo and received a suspended jail sentence. He was pardoned in 1997.
The probe has put the business practices of the chaebol -- big family-run conglomerates -- back into the spotlight.
Backed by state funds, the chaebol created the "Miracle on the Han" which transformed South Korea from a destitute war-shattered nation into the world's 13th largest economy.
But their excesses were partly blamed for the country's travails during the Asian financial crisis of 1997-1998.
Liberal groups say the current probe will enhance corporate transparency while business lobby groups want it wound up quickly.
Samsung wields enormous influence in South Korea. Group-wide assets are valued at 280.8 billion dollars and its exports were worth 66.3 billion dollars last year, more than 20 percent of the nation's total.