The business tycoons are expected to testify on how and why they donated large sums of money to two dubious foundations allegedly controlled by Choi.

Choi is currently standing trial over suspicions she coerced the country's top conglomerates to contribute some tens of billions of won to the foundations and attempted to funnel the money to her own firms.

President Park, awaiting the Constitutional Court's decision on her impeachment, has been named an accomplice by state prosecutors in the case, though she has avoided indictment as the president has immunity from prosecution.

Both Park and Choi have flatly denied the allegations.

Kim, Chey and Cho attended a parliamentary hearing over the case in early December, along with six other heads of major conglomerates. The business tycoons have all maintained that they did not seek any business favors in return for the money.

Lotte Group Chairman Shin Dong-bin, POSCO CEO Kwon Oh-joon and KT Chairman Hwang Chang-gyu are also known to have been designated witnesses, but when they will attend the trial has not yet been confirmed. (Yonhap)