Ader Investment, founded by Jason Ader, claims to collectively hold about 3 % of IGT's shares, the company said.
Ader Investment, which focuses on hospitality and real estate sectors, also plans to nominate Jason Ader to IGT's board. Jason Ader has been an independent director on the Las Vegas Sands board since April 2009.
The notice was submitted in conjunction with and on behalf of Mathewson, IGT said.
Ader Investment's proxy fight is the result of a long-running dispute between the company and Mathewson, who retired in 2003, IGT said.
New York-based Ader Investment was not immediately available for comment.
Shares of IGT, which has a market value of us$3.9 billion, were up marginally in after-market trading. They closed at us$14.68 on the New York Stock Exchange on Monday.