One of South Korea's richest businessmen, Kim Seung-youn, has been jailed for 18 months for abducting and assaulting workers in a karaoke bar.
Protesters outside the court demanded a stiff sentence for Kim
Kim, 55, chairman of the Hanwha Group, was convicted of attacking the men with the aid of his bodyguards, to punish them for scuffling with his son.
He admitted responsibility for much of the violence, but said his bodyguards took over when he "got tired".
The case has generated intense public interest in South Korea.
Heads of family-controlled business conglomerates like Hanwha - which has interests in petrochemicals, finance, insurance, construction and retail - wield huge power.
Courts have often been lenient with these business leaders, but correspondents say the ruling in Kim's case shows that the judiciary is becoming more even-handed when sentencing the rich and powerful.
Passing sentence at Seoul District Court, the judge, Kim Chul-hwan, said Kim Seung-youn had used his position to take revenge on the workers, carrying out the attacks in a "systematic manner".
"The violation of the law is big and is serious," said the judge.
During the trial, prosecutors told the court that this was a revenge attack after an incident involving the defendant's son, Kim Dong-won, a Yale University student.
Kim Dong-won, 22, was reported to have needed stitches for an eye injury sustained in a brawl with bar workers at the Seoul club.
Kim Seung-youn was said to have mobilised his bodyguards and local gangsters to take the off-duty bar workers to a mountainside construction site, where the revenge beating occurred.
The judge found the tycoon guilty of "beating the defenceless victims with a metal pipe, and threatening them with a stun gun," although none of the workers sustained serious injuries.
The court ruled that a jail sentence was inevitable.
Before being taken into custody, Kim Seung-Youn apologised, saying that he had lost his temper and hoped that foolish fathers like himself would think twice before following his actions.
Traditionally, senior Korean business leaders have enjoyed favourable treatment by the courts in consideration of their contributions to building the country's economy.
More recently, however, the courts have started to hand down heavier sentences on the business elite.
In February Chung Mong-koo, the chairman of Hyundai motors, was sentenced to three years in jail for breach of trust and embezzling company funds.
Mr Chung appealed earlier this year and prosecutors reacted by asking for his sentence to be increased to six years.