Agcom (Autorità per le Garanzie nelle Comunicazioni, Communications Authority) yesterday said the company now exerts excessive dominance over Italy's entertainment and telecoms markets - a claim disputed by Vivendi, which has declared its intention to seek legal action over the ruling.
The authority did not say how much Vivendi would need to divest in either company but ordered the French group to present it with a "specific plan of action" within 60 days.
Giordani said on Wednesday that Vivendi, which now holds a 28.8 percent stake in Mediaset, does have a relevant influence in the broadcaster's activities, in line with a ruling by an Italian regulator on Tuesday.
Italy's media laws grew partly out of parliamentary concerns in the 1990s over the combined political and business power of then prime minister and media tycoon Silvio Berlusconi, who remains the largest shareholder of Mediaset.
Bollore took almost a 30% stake in Mediaset a year ago, and slowly built a stake in Telecom Italia that's at 24%.
The French company - which according to its website, now holds 23.94 percent of Telecom Italia and 28.8 percent of Mediaset - expressed "astonishment" at the AgCom ruling and said it "reserves the right to bring legal action".
The French group said it reserved the right to appeal the decision at a regional court, and to submit a formal complaint with the European Commission.
AGCOM opened the investigation into Vivendi on December 21 2016 after Mediaset filed a complaint.
Mediaset has taken a hit of €341.3 million in its dispute with Vivendi over the sale of the Mediaset Premium.
ISS also urged Vivendi investors to vote against executive pay levels for the management board, including for CEO Arnaud de Puyfontaine.
Vivendi also has a 24% holding in Telecom Italia, one of the country's biggest telecommunications companies.