JIANGXI, China — Two Chinese labour activists were reported missing, with a third detained by police, while they were investigating labour violations at a factory that manufactured Ivanka Trump shoes, according to a workers advocacy group.

Hua Haifeng, Li Zhao and Su Heng, working undercover under the direction of New York-based China Labor Watch at a factory operated by shoe manufacturer Huajian Group in the southeast province of Jiangxi, have been unreachable by phone over the weekend, said Li Qiang, the founder of the advocacy group. Hua’s wife was contacted by local police by phone Tuesday afternoon and told that he’s been detained for illegal eavesdropping, said the wife, Deng Guimian.

Huajian’s facility is one of 15 factories that make products for the brand founded by the daughter of US President Donald Trump that China Labor Watch said it has been investigating in the past year. In a letter sent to Ivanka Trump in April, the group alleged a number of labour violations at two unnamed factories that supply the Ivanka Trump brand, including that employees were forced to work at least 12 1/2 hours a day for wages below China’s legal minimum — a monthly salary equivalent to about a dollar an hour.

Huajian representatives could not be immediately reached for comment at its factories in Ganzhou and Dongguan.

It’s the first time in 17 years that activists working for the non-profit workers advocacy group have been detained by the Chinese police, Li said. Hua was supposed to deliver evidence of violations including images and videos to Li in Hong Kong last week but was barred from leaving the country without being given a reason, Li said.

“I’ve been with my husband for 10 years and he has always been in this line. There’s never been any problems before,” Hua’s wife Deng, said by phone Wednesday. “He was working for justice and helping ordinary workers. I felt that what he did was not harming anyone, he was helping people.”

An Ivanka Trump representative declined to comment. A White House spokesman didn’t immediately respond to a request for comment. Calls to the Ganzhou Public Security Bureau went unanswered on Wednesday.

The factory also makes products for other brands including, Coach and Marc Fisher Footwear Co., according to the Chinese manufacturer's website. A Marc Fisher spokesman said the company is "unaware of the allegations and will look into them immediately."

Coach Inc. officials could not be reached for comment after local business hours.

By Stephanie Wong, with assistance from Rachel Chang Daniela Wei Keith Zhai and Lindsey Rupp; editors: K. Oanh Ha, Ken Wills.