The activist investor seeking changes at Buffalo Wild Wings Inc. launched a new offensive Thursday with his biggest demand of all: the resignation of Sally Smith, who built the company into a juggernaut over two decades as chief executive.

Mick McGuire, principal of Marcato Capital, since last summer has pushed Smith and the company’s directors to structure the firm more like its rival Wingstop Inc., which relies heavily on franchisees to own and operate restaurants.

After Smith and the board took steps three months ago to test McGuire’s structure, he ratcheted up his criticism to cover the Golden Valley-based company’s recent share performance and the record of executives’ stock purchases and sales.

His newest salvo came in a proxy statement and letter to shareholders designed at winning support for a slate of board candidates, including himself, at its annual meeting, expected next month.

“The status quo is unacceptable,” McGuire said in the letter. “Oversight and accountability must be restored and CEO Sally Smith must be replaced.”

Buffalo Wild Wings was one of the fastest-growing restaurant chains in the country from the late 1990s until the early 2010s. Its growth leveled off in recent years, though, and McGuire focused on that period in his criticism.

“Shares have underperformed virtually every relevant benchmark on a one-year, three-year, and five-year basis, and restaurant margins are at their lowest level since the financial crisis,” McGuire said in the letter.

He said Smith and other company executives were “seemingly out to lunch as the business has deteriorated.”

In response, the company issued a statement that cited its longer-term results.

“Over the past decade, Buffalo Wild Wings’ performance has consistently led the casual dining industry, delivering superior results to our shareholders while providing a differentiated guest experience to our customers,” the company said.

A person who invested $10,000 at the company’s initial public offering in 2003 would have $175,000 today, it noted. “The company has continued to innovate and pursue cost-savings initiatives amid difficult market conditions for the sector and remains focused on creating sustainable value for our shareholders,” the company added.

The company’s shares rose 6 percent Thursday amid the back-and-forth to $163.75, their highest level since December.

McGuire said in a CNBC interview Thursday that Buffalo Wild Wings shares would rise two to three times higher over the next three or four years if it lifted the profits of its company-owned stores, shifted more stores to franchisee ownership and lowered its capital costs.

“That type of value is only going to be achieved if the company executes on what we think are the critical value drivers,” McGuire said.

Buffalo Wild Wings owns about 600 of its 1,200 locations. McGuire wants the company to sell 90 percent of the company-owned stores to franchisees, saying that would reduce its corporate costs. Its own franchisee-run units produce higher per-unit profits than its corporate ones, McGuire said. He also cited the performance of Dallas-based Wingstop, which has about 1,000 restaurants and relies far more heavily on franchisee ownership.

“You can see how Wingstop itself has been able to be and grow by operating in a capital-light, franchisee-led model,” McGuire said on CNBC.

Buffalo Wild Wings earlier this year said it would sell about 60 of its company-owned locations to franchisees to test McGuire’s idea. Executives at the time, however, expressed doubt that a massive switch-over of ownership would yield the values for the properties that McGuire estimated.