Nokia's and Microsoft's launched their partnership last week. It enables Nokia to free up its software investment, and Microsoft to extend its mobile operating system market share.
The campaign, dubbed Nokia Plan-B, proposes ousting chief executive Stephen Elop, investing heavily in research and development, and scaling back the partnership with Microsoft to cover just North America.
It is not clear who is behind the campaign. The letter said: "We are a group of nine young Nokia shareholders. All of us have worked with Nokia in different capacities in the past."