But Ms. Trump did call in a speech at the State Department on Tuesday for strong action against countries where human trafficking occurs, in conjunction with the release of a United States government report that labeled China as one such country. That report particularly criticized the treatment of migrants in China, however, and not necessarily factory workers.
Two of the men — Li Zhao and Hua Haifeng — worked undercover in the giant Dongguan factory of Huajian International, a Chinese company that claims to make shoes worn by one in every 10 women in the United States. The factory has made a wide range of brands of shoes, but makes only the heels of Ivanka Trump-branded footwear.
The heels are then shipped north to a second Huajian factory in Ganzhou that assembles the shoes. The third investigator, Su Heng, worked undercover there off and on from March until he was detained by the Ganzhou police on May 27.
Mr. Li and Mr. Hua were also detained in Ganzhou because they had fled there to join Mr. Su after they became worried that the police were monitoring them in Dongguan.
China Labor Watch contends that Huajian requires its workers to labor up to 18 hours in a day, violating China’s regulatory limits on overtime, and that they were paid less than they had been promised when they agreed to work for the company. Zhang Huarong, the company’s founder and chairman, strongly denied in a lengthy interview at the Dongguan factory in December that Huajian had violated labor laws, and company spokesmen have reiterated that position since then.
The Ivanka Trump brand has said that the last batch of its shoes to be made by Huajian was in March. China Labor Watch contends that further batches were scheduled to be manufactured for the brand at the end of May and in June, and that its investigators had been planning to document the production of those shoes but were detained by the authorities days beforehand.