JPMorgan Chase & Co. quit working on Tianhe Chemicals Group’s planned $1 billion initial public offering in Hong Kong amid a U.S. probe into hiring practices, two people with knowledge of the matter said.

The U.S. bank gave up the mandate as questions arose over Joyce Wei, a former employee, whose father is Tianhe Chemicals chairman Qi Wei, the people said, asking not to be identified because the information is private. UBS AG, which is also advising on the IPO, hired Wei toward the end of last year, two people with knowledge of the matter said.

U.S. authorities are examining whether New York-based JPMorgan hired people in Asia so that their relatives in government would steer business to the firm, people with knowledge with the investigations have said. Gaby Abdelnour, former head of the bank’s Asia-Pacific business, was questioned by U.S. investigators about his knowledge of the hiring practices, a person briefed on the matter said last week. Abdelnour and the bank haven’t been accused of wrongdoing.

“Investment banks are super cautious at the moment,” Philippe Espinasse, a former head of equity capital markets for Asia at Nomura Holdings Inc. and author of “IPO: a Global Guide,” said by phone Monday from Hong Kong. “They might have quite a bit to lose by staying on the deal if there were a direct link between the company’s senior management and someone they employ.”

Marie Cheung, a Hong Kong-based spokeswoman for JPMorgan, declined to comment. Mark Panday, a spokesman in the city for Zurich-based UBS, declined to comment. Joyce Wei declined to comment and referred all future calls to other UBS personnel when she was contacted at the Swiss bank’s Hong Kong office.

The JPMorgan probe has escalated since the bank said in August the Securities and Exchange Commission had sought information on its employment of certain people in Hong Kong and client relationships. It’s withdrawal from Tianhe Chemical’s IPO was reported by Reuters earlier Monday.

The Chinese lubricant maker hired banks including Morgan Stanley to manage the IPO in Hong Kong, two people with knowledge of the matter said in July. A man who answered the phone at Qi Wei’s office in the northeastern city of Jinzhou refused to give his name, said the company hadn’t seen the story and declined to comment further.

JPMorgan ended plans to manage a Hong Kong share sale by China Everbright Bank Co. because the probe delayed an internal approval process, two people with knowledge of the matter said in November.

“How to get the mandate, what means are used to get the mandate, how to pitch the mandate and who should get involved in the mandate have all become sensitive issues now,” Ronald Wan, chief China adviser for Asian Capital Holdings Ltd., said by phone from Hong Kong. “Investment banks need to handle them with greater care.”

JPMorgan was the fourth-ranked advisor to Chinese companies on overseas stock sales and equity-linked transactions last year, data compiled by Bloomberg show.