NEW YORK (CNN/Money) - A former senior executive of Dynegy Corp. has sued the company, charging he was fired last year because he refused to cooperate with a plan to cook the company's books in 2000, the company confirmed Monday.

Bradley Farnsworth is seeking unspecified damages in the suit, filed in a Texas state court in Houston Friday.

Farnsworth, who served as Dynegy's controller and chief accounting officer from 1997 to early 2001, says he was pressured to change accounting methods to hide energy trading losses and boost profits, according to the lawsuit.

Shares of Houston-based Dynegy (DYN: down $0.46 to $1.66, Research, Estimates) tumbled about 20 percent Monday afternoon.

"We deny the allegations and intend to vigorously contest Mr. Farnsworth's claims," Dynegy spokesman Steven Stengel told CNN/Money Monday. "It is the company's opinion that Mr. Farnsworth's allegations are a disingenuous effort on the part of the plaintiff and its counsel to exploit Dynegy's current circumstances for financial gain."

Stengel said Dynegy's lawyers have seen the suit, adding that Farnsworth, as controller, had a legal obligation to report any concerns with the company's quarterly report filed on Nov. 14, 2000.

The Securities and Exchange Commission and the U.S. attorney's office already are investigating Dynegy's accounting and energy trading practices amid allegations of inflated sales and profit.

The investigation is just one of several into energy companies amid the recent collapse of Enron Corp., which was set to be purchased by Dynegy last year when allegations of accounting fraud were disclosed. Enron filled for bankruptcy in December.

Dynegy last week agreed to sell its Northern Natural Gas Pipeline for $928 million in cash to a company controlled by famed investor Warren Buffett, who has been buying assets of troubled companies recently.