The activists were working with China Labor Watch, a New York-based nonprofit, and investigating Huajian Group factories in the southern Chinese cities of Ganzhou and Dongguan.

The company has denied allegations of excessive overtime and low wages. It says it stopped producing Ivanka Trump shoes months ago.

A lawyer for one of the activists said all three men were being held at the Ganzhou City Detention Center in China’s Jiangxi province and that he had been blocked from seeing his client, Hua Haifeng, on Monday and Tuesday morning.

The lawyer, Wen Yu, said authorities at the detention center told him Monday that “an accident happened in Hua Haifeng’s cell,” without providing further details.

He said that after waiting more than eight hours Monday, he was allowed to see his client for “less than one minute.”

“I rushed to him and told him, ‘I’m the lawyer hired by your wife,'” he said. Then police took him away. Yu added that Hua looked fine and managed a smile before police escorted him out.

Yu said that he was told the case was being handled by a national security team, rather than a criminal police squad. “This is strange because it is a small case,” he said.

Up to now, the U.S. government hadn’t said anything about the fate of the men.

“We urge China to release them immediately and otherwise afford them the judicial and fair trial protections to which they are entitled,” said Alicia Edwards, a State Department spokeswoman.

Edwards would not confirm if the U.S. raised the issue directly with China, saying she couldn’t comment on diplomatic conversations. White House spokesman Josh Raffel declined comment.

Ivanka Trump’s brand has declined to comment on the allegations or the arrest and disappearances. Marc Fisher, which produces shoes for Ivanka Trump and other brands, has said it is looking into the allegations. 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 there.

China Labor Watch executive director Li Qiang says he lost touch with the activists late last month.

The group plans to publish a report alleging low pay, excessive overtime and possible misuse of student labor. 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.

The arrest and disappearances come as China cracks down on perceived threats to the stability of its 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.

Edwards said the U.S. remains concerned by “the pattern of arrests and detentions.” She said labor activists are instrumental in helping American companies understand conditions in their supply chains and holding Chinese manufacturers accountable under Chinese labor laws.