Sherritt filed its proxy circular on Monday, and in a letter to investors Chairman Harold Stephen assailed Armoyan as someone who has no experience in Sherritt's lines of business. Stephen also said that Armoyan has a poor track record on corporate governance matters and no credible ideas for creating value beyond what management is already doing.

"Between now and the proxy voting deadline, shareholders will likely be subjected to hollow rhetoric from the dissident," he said, urging shareholders to "cut through this noise, consider the qualifications of each group of director nominees and determine which directors will act in the best interests of Sherritt and all of its shareholders."

Sherritt is set to hold a special shareholders meeting on May 6 to elect its board. The nickel, oil and gas producer said the meeting was requisitioned by shareholders affiliated with Armoyan, including Clarke Inc (Toronto:CKI.TO - News), which together beneficially own some 5 percent of its shares.

Armoyan is the chief executive of Clarke, a Halifax, Nova Scotia-based investment holding company listed on the Toronto Stock Exchange.

(Reporting by Euan Rocha; Editing by Peter Galloway)