At least one Barnes & Noble (bks, +15.85%) investor has had enough of the bookstore chain’s languishing sales.

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…