Worth up to 22 billion euros ($23.79 billion) and blessed by the Italian government, the sale is a key plank of the strategy planned by TIM's head Pietro Labriola to revamp the telecoms firm.

Vivendi, which was seeking a higher price, has filed a complaint with a Milan court to challenge the TIM board's decision to sell the network without a shareholder vote.

In its complaint Vivendi had sought April 22 as the date to hold the first hearing on the case, a day before TIM's annual general meeting, sources have previously said.

TIM declined to comment. Vivendi was not immediately available.

($1 = 0.9249 euros)

(Reporting by Alfredo Faieta, writing by Elvira Pollina, editing by Gavin Jones)