“Ivanka’s brand should immediately cease its work with this supplier, and the Trump administration should reverse its current course and confront China on its human rights abuses,” Adrienne Watson, spokeswoman for the Democratic National Committee, said in a Wednesday email. Ivanka Trump must decide, she added, “whether she can ignore the Chinese government’s apparent attempt to silence an investigation into those worker abuses.”

Amnesty International called Wednesday for the release of China Labor Watch investigator Hua Haifeng, as well as his two colleagues, who are feared to have been detained.

The men were working with an American nonprofit group to publish a report next month alleging low pay, excessive overtime and possible misuse of student labor, according to China Labor Watch executive director Li Qiang, who lost contact with the investigators over the weekend. The investigators also witnessed verbal abuse, with one manager insulting staff about poorly made shoes and making a crude reference in Chinese to female genitalia, according to Li.

China Labor Watch has been exposing poor working conditions at suppliers to some of the world’s best-known companies for nearly two decades, but Li said his work has never before attracted this level of scrutiny from China’s state security apparatus.

The arrest and disappearances come amid a crackdown on perceived threats to the stability of China’s ruling Communist Party, particularly from sources with foreign ties such as China Labor Watch. Faced with rising labor unrest and a slowing economy, Beijing has taken a stern approach to activism in southern China’s manufacturing belt and to human rights advocates generally, sparking a wave of critical reports about disappearances, public confessions, forced repatriation and torture in custody.

China Labor Watch’s investigation also had an unusual target: a brand owned by the daughter of the president of the United States.

Ivanka Trump’s lifestyle brand imports most of its merchandise from China, trade data show. She and her father both have extensive trademark portfolios in China, though neither has managed to build up a large retail or real estate presence here. The sister of Jared Kushner, a Trump adviser and husband of Ivanka, traveled to China this past month to court investment from Chinese families for a real estate project in New Jersey.

“The eagerness of members of the family to do business in China while airbrushing very troubling human rights and labor rights records of the country is troubling,” said Nicholas Bequelin, East Asia director for Amnesty International. He said it is only a matter of time before it is known “to what extent business is trumping any kind of consideration of the diplomatic capital of the U.S. in promoting human rights, labor rights and democracy.”

White House spokeswoman Hope Hicks referred questions to Ivanka Trump’s brand. The Ivanka Trump brand declined to comment.

Abigail Klem, who took over day-to-day management when the first daughter became a White House presidential adviser, has said the brand requires licensees and their manufacturers to “comply with all applicable laws and to maintain acceptable working conditions.”

China tightened control over foreign NGOs starting this year by requiring them to register with state security. Chinese Foreign Ministry spokeswoman Hua Chunying said at a regular news briefing Wednesday that she was not aware of the arrest and disappearances. She said China welcomed international NGOs to carry out research, but added, “we also hope that NGOs can also observe Chinese laws and regulations and don’t engage in any illegal actions or behavior.”

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. The crime carries a penalty of up to two years’ imprisonment.

Li said China Labor Watch asked police about the Deng and the two other investigators, Li Zhao and Su Heng, on Monday but received no reply.

AP was unable to reach the other investigators’ families. China’s Ministry of Public Security and police could not be reached for comment Tuesday, which was a national holiday in China. Calls went unanswered Wednesday morning.

The men were investigating Huajian Group factories in the southern Chinese cities of Ganzhou and Dongguan. Su Heng had been working undercover at the Ganzhou factory since April, Li said.

In January, Liu Shiyuan, then spokesman for the Huajian Group, told AP the company makes 10,000 to 20,000 pairs of shoes a year for Ivanka Trump’s brand — a fraction of the 20 million pairs the company produces a year. A current spokeswoman for the company, Long Shan, did not reply to questions Tuesday or Wednesday morning.

Li said investigators had seen Ivanka Trump-brand merchandise, as well as production orders for Ivanka Trump, Marc Fisher, Nine West and Easy Spirit.

“We were unaware of the allegations and will look into them immediately,” a spokeswoman for Marc Fisher, which manufactures Ivanka Trump, Easy Spirit and its own branded shoes, said in an email Tuesday. Nine West did not respond to requests for comment.