In a letter to the firm seen by Reuters, Amber, which has teamed up with fellow Lagardere shareholder Vivendi to demand four seats between them on the board, nominated its founder Joseph Oughourlian as one of its three candidates.

Lagardere declined to comment.

The request cranks up a tussle over the loss-making company and Paris Match owner that has drawn two of France's richest businessmen into its wake.

Bernard Arnault, who runs luxury goods group LVMH, is investing in the personal holding company of Arnaud Lagardere, the firm's managing partner - effectively backing the firm and its bosses, which have brushed off Amber in the past.

But media group Vivendi, controlled by billionaire Vincent Bollore and which now has a 23.5% stake in Lagardere, last week sided with Amber, a 20% stakeholder, to seek board representation.

Amber and Vivendi want Lagardere to send its notice for a shareholder meeting within 15 days, and hold the event in the 50 days that follow, according to the letter. Amber said it would go to court if Lagardere refused.

In May, Lagardere succeeded in fending off Amber's attempt to revoke its directors and appoint new ones partly thanks to Vivendi, but relations have now soured.

Arnaud Lagardere was re-appointed to his top job earlier this week, seven months ahead of schedule, at a board meeting neither Vivendi or Amber had been aware of, people familiar with the matter have said.

One Lagardere board member, Aline Sylla-Walbaum, a top executive at auction house Christie's, resigned ahead of the vote, a separate source close to the situation said.

Online news site Wansquare, which first reported her resignation, said she had had reservations about prolonging the CEO's mandate. Sylla-Walbaum confirmed she had stepped down but declined to comment further.

(Reporting by Sarah White; Editing by Geert De Clercq, Kirsten Donovan)