The Stamford, Conn.-based paper and packaging manufacturer International Paper ( IP) said Thursday its board authorized a buyback of up to $3 billion of its stock. The buyback amounts to about 20% of the company's outstanding shares at Wednesday's closing price of $32.12. International Paper said it plans to begin the buyback in the third quarter of 2006 and intends to repurchase a significant amount of shares before the end of the year. The company also said it plans to spend about $6 billion to $7 billion to strengthen the balance sheet through debt repayment and potential voluntary cash contributions to its U.S. pension fund. The company said it is exploring selling its Tres Lagoas forestlands and mill site in Brazil to a buyer who would build, own and operate the pulp mill and is also exploring possible investments in China, Russia and North America. Shares fell a dime Thursday to $32.02.