J.C. Penney Co. (NYSE: JCP) said it has adopted a stockholder rights plan and declared a dividend of one right on each outstanding share of its common stock after activist investor William Ackman disclosed a significant stake in the apparel retailer.

A shareholder rights plan, colloquially known as a "poison pill," is a kind of defensive tactic used by a company to fend off potential takeover threats.

Under the rights plan, which will expire on Oct. 14, 2011, each right entitles the holder to buy additional voting rights of $130.00 per right, the company said.

The rights become exercisable if any person or group acquires 10 percent or more of J.C. Penney's common stock or, in the case of any person or group that currently owns 10 percent or more of the common stock, upon the acquisition of additional shares by such person or group.

"The Board adopted the rights plan, which has a term of one year, to promote fair and equal treatment of J.C. Penney's stockholders in connection with any initiative to acquire control of the company and in light of recent rapid accumulations of a significant percentage of the company's outstanding common stock," the company said in a statement today.http:/img.ibtimes.com/www/site/us/images/1px.gif

Earlier this month, regulatory filings showed that Pershing Square, the New York hedge-fund firm led by Ackman, snapped up a 16.5 percent stake in J.C. Penney that equals to 39 million common shares, including about 4.15 million options.

The firm plans to engage in talks with J.C. Penney's board and managers regarding the company's performance, according to the filing.

J.C. Penny said its board is committed to act in the best interests of all its stockholders.

Ackman generally acquires stock in companies he deems undervalued, particularly in the retail, restaurant and real estate industries, and urges strategic changes to boost shareholder returns.

Ackman has in the recent past acquired positions in Wendy's International Inc. (NYSE: WEN), McDonald's Corp (NYSE: MCD), General Growth Properties, Borders Group and Ceridian Corp., pressuring the management of those companies to improve profits by selling either real estate assets or corporate divisions.

Ackman will benefit when the asset liquidation returns capital in the form of dividends and a higher share price, whereby Pershing divests itself of its holdings at a higher share price.

In the case of Wendy's International, Wendy's management bought back shares following the forced sale of their subsidiary Tim Hortons through an IPO, while Pershing unloaded most of their shares.

In 2007, Ackman pushed for a share buyback at Target Corp. and lobbied restaurant chain Wendy's International to sell land after acquiring a 9.3 percent stake.

J.C. Penney sales have shrunk more than 40 percent in the past decade, and for the quarter ended July 2010, its sales remained flat with last year at $3.9 billion.

Barclays Capital Inc. and Goldman, Sachs & Co. are serving as financial advisors to J.C. Penney.

Texas-based J.C. Penney, one of America's leading retailers, operates over 1,100 department stores throughout the United States and Puerto Rico, as well as one of the largest apparel and home furnishing sites on the Internet, jcp.com.

Shares of J.C. Penney closed Friday's regular trading session at $33.87. In the pre-market hours Monday, they were down 1.36 percent at $33.41.

Try any of our Foolish newsletter services free for 30 days. True to its name, The Motley Fool is made up of a motley assortment of writers and analysts, each with a unique perspective; sometimes we agree, sometimes we disagree, but we all believe in the power of learning from each other through our Foolish community. The Motley Fool has a disclosure policy.