MILAN (Reuters) - A first hearing on the case filed by Telecom Italia's (TIM) top investor Vivendi against the sale of the former phone monopoly's fixed network to U.S. fund KKR has been scheduled for May 21, two legal sources told Reuters.

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)