Activist investor Sandell Asset Management on Tuesday made public its letter to the Barnes & Noble board urging it to try to sell itself, arguing that the retailer could fetch at least $12 per share and enjoy improving fortunes under new ownership.

Shares which have been floating around $7 of late, giving Barnes & Noble a valuation of about $500 million, rose to about $8, or a 14% increase in morning trading.

The investor, which according to the Wall Street Journal, recently built up a stake large enough to place it among Barnes & Noble’s top 10 investors.

Barnes & Noble spokesperson Mary Ellen Keating told Fortune in an email statement that Sandell had not reached out to the bookseller but that “we welcome constructive dialogue with all of our shareholders.”

Having shed its college bookstore chain two years ago and downsized its Nook business, Barnes & Noble now has only its main retail business to rely on for growth. But the company has been trying to revitalize its retail business with little success so far. Despite a maturing of the e-books market, where growth now mirrors that of physical books, comparable sales declined 6.3% in the fiscal year finished at the end of April and the bookseller expects a modest decline this year.

What’s more, e-commerce growth has been anemic, a dangerous weakness at a time Amazon.com (AMZN) is opening bookstores. And there has been quite a bit of turnover in the c-suite: in April, Barnes & Noble named Demos Parneros to be its CEO, the fourth person to fill the role in as many years.

In an interview with Fortune in May, Parneros said Barnes & Noble was looking at smaller formats and testing different ideas, expanding its in-store cafe service to include options like wine, and tweaking its merchandise. But it’s not clear when such efforts, at a handful of stores, will be enough to move the needle for the 634-store chain, assuming they are successful.

Parneros, a longtime Staples (SPLS) veteran, did not signal any radical moves to re-energize what remains the largest bookstore chain. But Sandell made the argument Barnes & Noble should be owned by investors ready to pump money into its operations.

In a letter to the Barnes & Noble board dated July 25, Thomas Sandell, the firm’s CEO, blasted the retailer’s founder, chairman, ex-CEO and top shareholder Leonard Riggio for the retailer’s woes. “One need only focus on Mr. Riggio’s inability to reposition Barnes & Noble as a vital strategic retail asset for the vibrant information economy of the 21st Centure to see how he has let shareholders down,” Sandell wrote, after listing what he saw as the retailer’s failings on Riggio’s watch.

This isn’t the first time Barnes & Noble has faced off with an activist investor. It defeated billionaire Ron Burkle in a proxy war in 2009. Nor would it be the first time the chain tried to sell itself. In 2010 it announced a sales process. A year later, in 2011, John Malone’s Liberty Media Corp offered $1.02 billion but later instead only invested $204 million and got two board seats. And in 2013, Riggio said he might buy the chain’s retail business but ultimately dropped that plan.