"We appeal to President Trump, Ivanka Trump herself and to her related brand company to advocate and press for the release of our activists", Mr Li said. Huajian meanwhile, the company running the factory in China, its spokesman Wei Xuegang said he was not aware of any arrests, according to the Post.
The key question in light of the organization's apparent track record of never having run-ins with the law is whether Chinese authorities were more likely to crack down on the investigators in an attempt to curry favor with the Trump administration.
Chinese President Xi Jinping has relentlessly clamped down on activism and civil society groups since he came to power in late 2012.
Huajian has previously said it has been making shoes for the USA president's daughter for almost a decade, accounting for one-third of her shoes made in China but only a small proportion of its total output.
Both factories produced Ivanka Trump shoes, Mr Li said.
The news comes amid a broader crackdown in China on independent groups pushing for better labor rights in the world's second-largest economy.More news: IS seals off area of symbolic mosque in Mosul's Old City
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Out of office hours calls by TIME to the Ivanka Trump brand went unanswered at time of publication. The group said that the supplier also makes products for other Western brands including Karl Lagerfeld, Coach and Nine West.
The three activists said they found workers were subject to exceptionally long working hours in their preliminary findings, which had not yet been made public. The companies didn't immediately respond to requests for comment.
President Donald Trump has always urged USA companies to manufacture their products in the country.
A woman surnamed Mu, who said she was in charge of recruitment at Huajian, said she had not heard about the case. She said that Hua Haifeng joined the group's factory in Dongguan on May 20, but left after less than a week, and Su Heng began working at their Ganzhou factory on April 28, but also left after a short time.
CLW said that Hua was detained in the Jiangxi province on suspicion of illegally using eavesdropping equipment but allegation had "no factual basis".
The group were probing Ganzhou Huajian International Shoe City Co.'s in China's Jiangxi province, which is owned by parent company Huajian Group. During their final phone conversation on Saturday, Hua told Li that police had asked him to stop investigating the Huajian factory - another turn of events that Li said was unprecedented. I feel his work is legal and meaningful.