UBS is advising some of its bankers against travelling to China.

UBS has warned some of its bankers against travelling to China after the country asked one of the Swiss lender’s managers to assist an investigation, media reports said, citing unnamed sources.

The nature of the investigation and why the authorities want to speak to the banker – a woman who had been based in Singapore but is now in Beijing – isn’t known, a source told the Wall Street Journal. The unnamed source said the woman is not facing a legal issue herself and expected to talk to legal authorities in coming days. Separately, Bloomberg said a UBS employee had been “detained”.

The WSJ’s story said UBS’ warning to employees applies only to wealth managers for the firm and advises that they consider holding off China travel for a few days as more information becomes available.

The name of a female UBS wealth manager was widely circulated on social media in China over the weekend in a message that said she wasn’t permitted to leave the country this past week, the report said. Singapore’s embassy in Beijing and its Ministry of Foreign Affairs didn’t immediately respond to questions, the WSJ said.

Such a restriction on travel to China will be a blow to a bank that has aggressively stepped up Asia operations in recent years, as have Swiss rivals Credit Suisse and Julius Baer.

UBS declined to comment to this news service when contacted today.