The probe is meant to establish whether Vivendi, as an investor in Italy's media and telecoms sectors, complies with rules designed to protect media plurality and follows a stop-gap legislation Rome approved last month.

The law, which prompted the need for an AGCOM inquiry and could result in curbs to Vivendi's assets in the country, has raised concerns with the European Commission.

The Commission has written a letter to Italy's industry minister asking for the bill to be notified with the EU, according to another source close to the matter.

AGCOM's meeting, originally planned for Monday, was postponed after watchdog officials were kept busy longer than expected with other planned activities, the first source said.

The regulator's probe could help Mediaset, controlled by the family of former Prime Minister Silvio Berlusconi, in a long running dispute with Vivendi, its second largest shareholder, whose investment Mediaset considers hostile.

Vivendi has lodged a formal complaint with the EU on the stop-gap law, saying it was aimed at circumventing a EU top court decision in September, which had virtually returned the French group full voting rights on its stake in Mediaset.

(Reporting by Elvira Pollina and Giuseppe Fonte; Editing by Alison Williams)