The investment company of Italian Prime Minister Silvio Berlusconi has been ordered to pay $801 million to a rival business venture after it bribed a judge to win approval of the takeover of a publishing company.

A Milan appellate court on Saturday upheld a 2009 lower court ruling against Mr. Berlusconi's Fininvest company, although it did cut the damages by a quarter. Mr. Berlusconi's daughter, Marina Berlusconi, who chairs Fininvest, called the decision a “totally unjust verdict” and said it would appeal to the nation's highest court.

The civil damage award is the latest twist in Fininvest's two-decade-old effort to take over the Mondadori publishing company in a fight with Compagnie Industriali Riunite, the conglomerate run by Mr. Berlusconi's arch-rival, Carlo De Benedetti. In a 2009 decision, a judge ruled that Mr. Berlusconi was “co-responsible” in the bribery of a judge who ruled in favor of Fininvest in the corporate takeover battle.

The judge linked to the bribery was sentenced to nearly three years in prison while a Fininvest lawyer who bribed him was handed a year-and-a-half term.

The appellate court ruling was the second setback this week for Mr. Berlusconi connected to the Mondadori acquisition.

The prime minister was sharply criticized when he introduced a measure into Italy's austerity budget that would have allowed Fininvest to delay payment of the civil judgment until the final appeal decision had been handed down. He said it would protect companies against “erroneous” judgments.

But after his political opponents attacked his plan, and even allies said they were unaware of it, Mr. Berlusconi retreated and withdrew the proposal.

Mr. Berlusconi is facing other legal difficulties as well. His trial alleging that he paid for sex with an underage teen and then tried to cover it up is scheduled to resume later this month.