Shares of Shake Shack (NYSE: SHAK) were climbing today on reports that an activist is circling around the fast-casual burger chain and planning a proxy battle for three board seats. According to The Wall Street Journal, Engaged Capital has been in talks with Shake Shack management for more than six months, and proposed to install new directors and make other changes that it thinks would boost the stock price. The two sides appear to be at an impasse, and Shake Shack said in a statement that it is making financial progress on its strategic plan.