BEIJING (AP) — A vice mayor of China's financial hub of Shanghai is under investigation by the ruling Communist Party amid an ongoing drive against corruption at all levels of government.

Ai Baojun was being probed on suspicion of "serious violations of discipline," the party's Central Commission for Discipline Inspection said on its website Tuesday. The phrase almost always refers to corruption.

Ai's name had already been removed from the list of Shanghai vice mayors, a likely sign that he will soon be fired and expelled from the party as a precursor to prosecution.

The 55-year-old Ai was appointed a vice mayor in 2007, and two years ago became director of the city's new Hong Kong-style free trade zone that has been heavily promoted by the central government. Trained as an accountant, Ai had also been chairman of Baoshan Iron and Steel Co. Ltd., the listed unit of Shanghai's massive Baosteel Group Corp.

Thousands of officials have been investigated under the anti-graft campaign that President Xi Jinping launched shortly after taking office two years ago. More than 100 senior officials and military officers have been placed under investigation or charged criminally, with no sign yet of the campaign abating.