A bipartisan group of lawmakers has taken the Trump administration to task for its “inadequate response” to China’s alleged “inhumane persecution” of Uighurs, a Muslim ethnic minority, in the province of Xinjiang.

In a letter addressed to Secretary of State Mike Pompeo, the lawmakers — led by Rep. Eliot Engel (D-N.Y.), chairman of the House Committee on Foreign Affairs — upbraided the administration for not taking “meaningful action” against Beijing despite allegations that President Xi Jinping’s government had “systematically” denied Uighurs “their basic freedoms and created programs of mass surveillance and internment.”

“The United States must stand up for the oppressed and, at every opportunity, make clear to the Chinese government that the situation in [Xinjiang] is a priority for the U.S. Government,” the letter reads. “This issue is bigger than just China. It is about demonstrating to strongmen globally that the world will hold them accountable for their actions.”

Rep. Brad Sherman (D-Calif.), Rep. Ted Yoho (R-Fla.), the chairman and ranking member of the Subcommittee on Asia, the Pacific and Nonproliferation; and Rep. Chris Smith (R-N.J.), ranking member of the Subcommittee on Africa, Global Health, Global Human Rights and International Organizations, also signed the letter.

The lawmakers noted that they wrote to the State Department four months ago about this very issue, but nothing substantial had been done.

“We write today with a renewed sense of urgency on this serious matter,” they wrote.

“Of particular concern are reports of U.S. companies that may be contributing to Beijing’s persecution of Uighurs through their support or commercial ties to Hikvision and Dahua — two Chinese tech giants that have profited from the surge of security spending in Xinjiang,” the lawmakers said.

They also expressed alarm at a Reuters report published in January that said Frontier Services Group, a company backed by former Blackwater CEO Erik Prince, was building a “training facility” in Xinjiang.