Activist investor Engaged Capital has built a 6.6% stake in Shake Shack, including swaps, and is planning to run a proxy fight for three board seats, Lauren Thomas of Wall Street Journal reports, citing people familiar with the matter. Engaged has been in talks with Shake Shack’s management for over six months but the two sides have thus far failed to reach an agreement, sources the Journal. The activist sent a letter to the company’s board in March detailing its proposal for new directors and other changes to help boost its stock price, they added. :We are executing our strategic plan and making substantial operational and financial progress,” a spokesman for Shake Shack said in a statement to the paper. “We are well positioned to continue enhancing value for shareholders.”