PARIS-- Vincent Bolloré boosted his stake in Vivendi SA for the third time in a month as a public quarrel with its shareholder P. Schoenfeld Asset Management LP is heating up.

Groupe Bolloré, the conglomerate controlled by Mr. Bolloré, said Thursday it has increased its stake in Vivendi to 12.01% from 10.2% after purchasing 24.6 million more shares for a total of EUR568 million ($615 million).

The move comes as Vivendi is under fire from PSAM, which wants Vivendi to use funds from recent asset sales to boost shareholder returns. PSAM has proposed two resolutions to that end for Vivendi's general meeting later this month and is trying to rally support from other shareholders in its push.

Vivendi has been fighting back. The French owner of pay TV group Canal Plus and Universal Music Group argues that PSAM, which owns 0.8% in Vivendi, wants to dismantle the company and is urging shareholders not to vote for PSAM's resolutions.

Mr. Bolloré, who took over the chairmanship of Vivendi last June and is also Vivendi's largest individual shareholder, has more than doubled his holding in Vivendi over the past month.

Write to Ruth Bender at Ruth.Bender@wsj.com

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