NEW YORK --The proposed takeover of Dynegy Inc. by billionaire investor Carl Icahn received the final regulatory approval needed Friday, as some shareholders continued to fight the deal. The Federal Energy Regulatory Commission has cleared the way for the proposed acquisition by Icahn Enterprises LP, the company's largest shareholder. Icahn has offered of $665 million for Houston power producer and Dynegy's board already has accepted Icahn's offer of $5.50 per share. However, Seneca Capital, Dynegy's second-largest shareholder has been vocal in its opposition to the deal. A special committee of Dynegy's board sent shareholders a letter Friday criticizing Seneca for distributing what the committee said was misleading information with "exceedingly wishful assumptions about power markets." The committee said a continued slump in natural gas prices has tugged power prices lower since last summer, making it tough for the company to pay off debt. Accepting Icahn's offer is the best outcome for Dynegy, it said. "You have an opportunity to decide whether Dynegy should sell itself to a financially stronger entity and provide all stockholders with a known value today, or alternatively, continue to work through significant financial challenges," the letter said. Earlier this week, Icahn extended his offer so that it now will expire on Monday. About 5.4 million shares, or 4.4 percent of outstanding Dynegy stock, have been tendered in support of the deal. At least 50 percent of Dynegy shares must be voted in favor of the sale for the deal to go through. Dynegy's shares slipped 4 cents, to $5.70 in afternoon trading Friday.