Bookseller Barnes & Noble ( BKS) said the Securities and Exchange Commission has started an informal inquiry into the company's stock option grants.

On Friday, the company filed a short document with regulators saying that it plans to cooperate fully with the SEC's investigation. Barnes & Noble was already conducting an internal review of its option practices.

Last week, Barnes & Noble said a shareholder filed a lawsuit alleging improprieties in the company's issuance of stock options. The company said it believed there was no merit to the complaint "and that its practices with respect to the issuance of stock options have always been entirely appropriate and in full compliance with all applicable laws and regulations."

Still, its board decided to have the audit committee and independent attorneys review its option program.

Dozens of companies, many of them in the tech sector, are conducting probes or reporting that authorities are looking into their options plans, often for the practice of backdating. SEC Chairman Christopher Cox said Thursday at a press conference that his agency is currently examining backdating allegations at more than 80 companies.

Options give the holder the right to buy the underlying stock at a predetermined price. Generally, under company plans, the exercise price would be the market price of the stock on the date the options are granted.

However, companies in the expanding backdating scandal are alleged to have handed out options that carried exercise prices from dates before the actual grant date. In many cases, the exercise prices corresponded to short-term lows in the stocks. The more a stock moves above the exercise price of the option, the more money the option holder stands to gain.