Chicago’s hometown hot dog giant Portillo’s is in the midst of an ambitious national expansion, and now a proxy fight may be brewing in its boardroom.

A big shareholder in Portillo’s is engaging the Chicago restaurant chain in a fight to add two board seats, claiming its performance “appears to be suffering.”

Activist investor Engaged Capital is ready to run a boardroom fight at restaurant chain Portillo's and has nominated two director candidates to the company's eight-member board, three people familiar with the matter said.

Engaged Capital already installed the former Chipotle CFO to Portillo's board and is now getting aggressive to secure a seat for former Wingstop CEO Charlie Morrison.