UPDATE 2-Italian watchdog opens inquiries into Vivendi, SKY telecoms and media assets

* Probe could help Mediaset in dispute against French group

* Vivendi complained to EU over law giving watchdog new powers

* Regulator also to investigate Comcast unit’s assets (Adds Vivendi declines comment, length of inquiry)

MILAN, Dec 15 (Reuters) - Italy’s communications watchdog AGCOM said on Tuesday it had opened an inquiry into French media giant Vivendi’s stakes in commercial broadcaster Mediaset and the country’s biggest phone group Telecom Italia (TIM).

Vivendi is TIM’s biggest shareholder with a 23.9% stake and Mediaset’s second-largest with a 28.8% holding although its voting rights in the broadcaster have been curbed to 10%.

AGCOM said in a statement it had launched a similar probe into SKY Italia’s telecoms and media assets. SKY, part of Comcast, is a major player in Italy’s pay-TV market and has recently launched its own broadband services.

Both inquiries would last four months, the regulator said.

Vivendi declined to comment. SKY did not respond to a request for a comment.

AGCOM’s inquiry could help Mediaset, controlled by the family of former Prime Minister Silvio Berlusconi, in its battle against Vivendi as the French group tries to recover its voting rights for its full stake in the broadcaster.

The two groups have been at loggerheads since 2016 when Vivendi ditched an accord to buy Mediaset’s pay-TV unit and built its 29% stake, which Mediaset considers hostile.

Vivendi was forced to transfer two thirds of its voting rights in Mediaset into a trust after Italy’s communications watchdog ruled in 2017 that it had broken media plurality rules.

The trust has been prevented from voting at Mediaset’s shareholder meetings.

In September, however, the European Union’s top court ruled the Italian law in question violated EU rules.

That prompted Rome to approve stop-gap legislation which requires AGCOM to hold an inquiry into whether Vivendi’s positions in Italy’s telecoms and media sectors are harmful for media plurality by looking at total revenues, entry barriers and the level of competition in those sectors.

The probe could delay an administrative court decision on Vivendi’s request to scrap restrictions on its Mediaset holding, legal sources have said. A hearing on the case is set for Dec. 16.

On Friday, Vivendi lodged a complaint with the European Commission against the stop-gap law, saying it was aimed at circumventing September’s EU court decision. (Reporting by Giuseppe Fonte and Elvira Pollina; Editing by Mark Potter and Timothy Heritage)