New York (CNN Business) Billionaire investor Carl Icahn is furious over the generous terms Warren Buffett received when he came to the aid of Occidental Petroleum's bidding war with Chevron.

Buffett'sagreed in late April to provide $10 billion in equity financing to add firepower to Occidental's controversial hostile takeover offer for

"The whole thing is a travesty," Icahn, who is launching an increasingly-contentious proxy war to replace fourdirectors, told CNN Business.

If oil goes below $40 a barrel, the Anadarko deal could give Occidental almost an existential problem."

Icahn, a fierce critic of the Anadarko acquisition , took particular issue with the decision by Occidental CEO Vicki Hollub to grant Buffett warrants to purchase up to 80 million shares of common stock.

"She gave him a gift," Icahn said of Hollub, adding that others would have done the deal a lot more cheaply.

However, the activist investor made clear he is not criticizing Buffett for the deal.

"I certainly don't blame Warren -- I blame the OXY board and Hollub," Icahn told CNN Business, using the oil company's stock ticker. "This is the poster child for what is wrong with corporate governance."

"Buffett figuratively took her to the cleaners," Icahn wrote, adding that the deal was "like taking candy from a baby."

Buffett's Berkshire Hathaway did not respond to a request for comment. Occidental declined to comment, but the company has previously explained that it didn't have the luxury of waiting to get the funds it needed from Berkshire.

Board battle gets ugly

Occidental fired off its own sharply worded letter on Monday urging shareholders to reject Icahn's effort to replace four directors, including Chairman Eugene Batchelder. Occidental defended its acquisition of Anadarko -- a deal aimed at expanding the oil giant's presence in the booming Permian Basin of West Texas.

"Mr. Icahn's own statements demonstrate that he does not understand or support the strategic and financial merits of the acquisition," Hollub and Batchelder wrote in the letter.

The executives warned that Icahn's nominees for the board would "interfere" with Occidental's ability to successfully integrate Anadarko's "valuable assets and deliver on the promise of this acquisition at this critical juncture."

Icahn's board slate includes former Jarden finance chief Alan LeFevre, former Shell Oil Company president John Hofmeister and two of his firm's executives.

Occidental argued in the letter that "none" of Icahn's proposed directors "possess skills, experience or expertise that are additive or superior to our existing directors."

Still, some large Occidental shareholders and analysts have echoed Icahn's concerns about the structuring of the Anadarko acquisition.

'Existential' threat to Occidental?

While Occidental has championed the Anadarko deal as a smart way to capitalize on the US shale oil boom, Icahn fears the acquisition is too risky. He points to the volatile nature of oil prices and the added leverage Occidental had to take on to get its hands on Anadarko.

"If oil goes below $40 a barrel, the Anadarko deal could give Occidental almost an existential problem," Icahn told CNN Business.

Occidental has promised to rapidly reduce its debt, in part by selling off some of its non-oil assets. Occidental also projects the acquisition will generate at least $3.5 billion in annual cost and capital spending synergies -- giving the company further flexibility to clean up its balance sheet.

Icahn, who Forbes estimates has a net worth of $18.6 billion , also took issue with Occidental's executive compensation practices.

"They have to work two years to earn what she makes in one week," Icahn told CNN Business. "What is she making it for? Losing $18 billion in market cap?"

Occidental has said in filings that Hollub's 12% increase in stock awards to $9.5 million was "appropriate in recognition" of her 2017 performance. The company also said the pay boost was designed to "better align" Hollub's compensation with her peers.