Activist shareholder Schuster Tanger has urged Capital Senior Living Corp. to hire an investment firm to enact major changes at the firm, including a possible sale.

Tanger’s letter says the operator remains undervalued. Capital Senior Living operates 121 communities with a capacity of approximately 15,400 residents. Tanger said selling the firm to a private-equity suitor or other buyer could fetch shares in the $32-to-$35 range. At midday Thursday, company stock was trading at $22.24 per share.

“Despite your best efforts and improved operational performance, the public markets are not affording the company credit for your pipeline, portfolio, and management business,” Tanger wrote. Although the firm has delivered recent earnings and operational improvements, Tanger said more needs to be done: “The fact that a company has favorable prospects is hardly a reason not to explore a value-maximizing transaction.”

He gave Capital Senior Living until mid-January to respond. The hedge fund operator has been co-managing member of Red Alder Master Fund, L.P. since September 2012.