Aegis, which owns media agencies Carat and Vizeum and research company Synovate, said it had received a joint letter from the majority shareholders, including Fidelity International, Standard Life and Henderson Global Investors in opposition to Bollore's request.
Bollore is trying to win two seats on the board for his representatives Roger Hatchuel and Philippe Germond, but has been blocked at every turn by Aegis despite owning 29% of the company.
The letter backing the Aegis board and its chief executive Robert Lerwill comes just before an extraordinary general meeting of the group set to take place on November 22 to consider the request.
The letter reads: "We note that the resolutions are identical to those proposed and voted down at the annual general meeting less than six months ago. In that vote, 45% of all Aegis shareholders voted against the two resolutions proposed, with 94% of the votes not controlled by Groupe Bollore being cast against. We regret that the company is being obliged to face the same resolutions again so soon."
It continues: "We retain our previous view that the resolutions are not in the interests of the company's shareholders as a whole and should be voted against. Board nominations by a shareholder who has significant influence at a direct competitor to the company are not appropriate, no matter how large that shareholder's interest in the company.
"We believe that this is a sufficiently important matter of corporate governance to merit making the contents of this letter public."
Aegis also said that the content of the letter was backed by six other shareholders. In total, the institutions account for 23% of Aegis equity.
Lord Sharman, chairman of Aegis, called for shareholders to vote against the request from Bollore.
"It is highly unusual for institutional shareholders to express their views so publicly, uniformly and clearly, well ahead of a vote. This reflects the strength of their feeling on the point of principle involved, as well as their frustration at the time and expense for all parties so soon after the annual general meeting. 70% of our shares are in the hands of investors other than Groupe Bollore.
"We urge every one of these shareholders to follow the lead set by our largest institutions by voting to defeat these resolutions."
This week Havas reported revenue growth of 0.6% to €343m (£230m) in the third quarter, during which it won the whole of Reckitt Benckiser's $1.5bn (£790m) global business and won Danone's $100m US media account.
In September, Aegis reported a strong set of results for the first half of the year, with profits up almost 9%.
The group saw its underlying pre-tax profits increase to £38m in the first six months of the year, up 8.9% from £34.9m in the same period last year.
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