The activist investor seeking strategic changes at Supervalu Inc. on Tuesday nominated six outside directors to be voted on by shareholders at the company’s annual meeting.

The move by Blackwells Capital LLC is the most aggressive yet since it revealed last fall that it had taken a sizable stake in the Eden Prairie-based grocery wholesaler and retailer, whose chains include Cub Foods, the market leader in the Twin Cities.

The investment firm last October urged Supervalu to sell at least one-third of its grocery stores and, in February, called for a breakup of the firm into separate wholesale and retail businesses.

In a proxy statement, Blackwells cited the declining performance of the company’s stock price over the past six years as a key reason to overhaul the company’s board. Shares are trading around $15, less than one-fourth of a 2015 peak. They closed up 1.3 percent to $18.21 on a day when the broader market fell.

“Supervalu is one of the most cheaply valued of all consumer staples public companies despite significant, tangible advantages, especially in relation to its direct competitors,” Jason Aintabi, managing partner for the New York-based investment firm, said in a statement.

In the proxy, Blackwells said it believes that the directors it nominated and the strategy it promotes will lift Supervalu’s share price to at least $45. The company “has opportunities to review strategic alternatives that can substantially accelerate its ability to unlock shareholder value,” Aintabi also said in his statement.

Supervalu earlier this year called the criticism by Blackwells “unnecessary and counterproductive” and noted steps it has taken to bolster its profitable wholesale business and lower costs on its retail side. Most recently, the company in March moved to sell 21 of its 38 Farm Fresh stores and, in April, said it would close some distribution centers.

On Tuesday, the company said: “Supervalu’s board and management team continue to rapidly execute our transformation strategy, which is well underway and includes the recent sale and lease-back of eight distribution centers, and the exit of our Farm Fresh banner, among other significant milestones. We remain confident in our transformation strategy and approach.”

The Blackwells nominees to the Supervalu board include Richard A. Anicetti, former chief executive of Fresh Market Inc. and, before that, Food Lion LLC; Steven H. Baer, partner in High Ridge Partners, a Chicago investment firm that specializes in turnarounds; and R. Chris Kreidler, former chief financial officer at Sysco Corp., the food-service giant.

It also nominated Frank Lazaran, former chief executive of Marsh Supermarket and Winn-Dixie Stores; James J. Martell, former FedEx executive and board member at several logistics firms; and Sandra E. Taylor, a consultant on social responsibility and former senior vice president of corporate responsibility at Starbucks Corp.

Supervalu hasn’t announced its shareholder meeting yet but will “in due course,” a spokesman said. The company last year held the meeting in July and sent out its proxy and related materials to shareholders in early June.