Biogen Idec Inc
Both Proxy Governance Inc and Glass, Lewis & Co have said stockholders should choose the company's slate and reject those proposed by Icahn, Biogen said.
It added that another firm, RiskMetrics, did not recommend the company's slate.
In his second proxy fight for board representation at Biogen, Icahn wants Biogen's board to consider splitting the biotechnology company into one firm focused on neurology and another focused on cancer.
Icahn also wants Biogen to examine its cost structure and improve its relationships with its partners.
Biogen will hold its annual shareholder meeting on June 3.
Last year, Icahn lost a proxy fight against Biogen. He had accused the Cambridge, Massachusetts-based biotech of sabotaging its own announced attempt to find a buyer.
(Reporting by Franklin Paul; Editing by Jan Paschal)