OREANDA-NEWS. September 06, 2013. China widened its anti-corruption campaign to include the nation’s biggest company by market value, as PetroChina Co. said three senior managers resigned and were under investigation by authorities. Its shares dived.

The managers, including top executives at two PetroChina units, are “currently under investigation by relevant PRC authorities,” the Beijing-based company said yesterday in a statement. The three are Li Hualin, chairman of Kunlun Energy Co., an oil and gas producer and distributor; PetroChina vice president and general manager of its biggest oilfield, Ran Xinquan; and Wang Daofu, chief geologist for PetroChina. The head of the company’s second-biggest oilfield has also being replaced, spokesman Mao Zefeng said.

“The only precedent we can think of here is back in 2007 when Sinopec’s Chairman Chen Tonghai was arrested,” said CLSA analyst Simon Powell in a note to investors. Chen, former chairman of the nation’s second-biggest oil company, China Petroleum & Chemical Corp., or Sinopec, received a suspended death penalty in 2009 for taking bribes.

The probes at PetroChina come amid a wider crackdown by China’s top leadership against official corruption that President Xi Jinping, who assumed power in March, has said threatens the communist party’s grip on power. The highly-publicized trial of former Politburo member Bo Xilai on bribery, embezzlement and power-abuse charges has been highlighted by the party as proof of its determination to target graft.