SHANGHAI (CBS NEWS) -- A man investigating working conditions at a Chinese company that produces Ivanka Trump-brand shoes has been arrested and two others are missing, the arrested man's wife and an advocacy group said Tuesday.

CBS News confirmed through China Labor Watch that the three men working for them investigating labor conditions at a Chinese company that also produces Ivanka Trump shoes have disappeared.

Hua Haifeng was accused of illegal surveillance, according to his wife, Deng Guilian, who said the police called her Tuesday afternoon. Deng said the caller told her she didn't need to know the details, only that she would not be able to see, speak with or receive money from her husband, the family's breadwinner. She said she didn't know her husband's whereabouts and hadn't spoken to him since 4pm Sunday, May 28.

China Labor Watch Executive Director Li Qiang said he lost contact with Hua Haifeng and the other two men, Li Zhao and Su Heng, over the weekend. By Tuesday, after dozens of unanswered calls, he had concluded: "They must be held either by the factory or the police to be unreachable." Officials at the Public Security Bureau in Ganzhou would not confirm to CBS News if Hua was detained, but his wife was made aware of the charge Tuesday afternoon.

China Labor Watch, a New York-based nonprofit, was planning to publish a report next month alleging low pay, excessive overtime and the possible misuse of student interns. It is unclear whether the undercover investigative methods used by the advocacy group are legal in China.

For 17 years, China Labor Watch has investigated working conditions at suppliers to some of the world's best-known companies, but Li said his work has never before attracted this level of scrutiny from China's state security apparatus. This is the first time anyone from China Labor Watch has been detained or prevented from leaving the country.

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