The US Customs and Border Protection (CBP) said imports from Serbia Zijin Copper had been halted as of Tuesday, arguing that US firms faced unfair competition from companies using forced labour.
The CBP said the firm breached workers' rights by withholding wages, intimidating them, restricting their movement and confiscating their identity documents -- among other claims.
The firm, which employs more than 6,000 people in Serbia, was established in 2018 after China's Zijin Mining acquired a 63-percent stake in the former state-owned RTB Bor.
It is the only company in the Balkan nation producing copper and precious metals such as gold and silver -- though its output is small by global standards.
In 2025, it produced 296,000 tons of copper and 9.1 tons of gold.
"The company is currently conducting a comprehensive review and assessment of the relevant issues, in line with its longstanding commitment to lawful and compliant business operations, as well as to the continuous improvement of protections for labour rights," Zijin said in a statement to AFP.
The CBP said in a statement its decision came after an investigation that analysed "worker statements, photographs, focus group field notes, text message screenshots, open-source non-government organisation reports, news media, and academic research".
"US manufacturers face unfair competition when foreign companies cut costs by using forced labour," the statement quoted Susan Thomas, CBP executive assistant commissioner, as saying.
"By enforcing our laws against forced labour, CBP safeguards human rights as well as our nation's economic security."
NGOs and independent investigations have warned about working conditions at the company.
In 2021, investigative outlet BIRN uncovered serious labour law violations affecting Chinese nationals working at the company, notably restrictions on freedom of movement, 12-hour workdays, and passport confiscations.
And local residents have regularly raised concerns about the mine's environmental impact.
In recent years, China has poured billions of dollars into Serbia and neighbouring countries, as Beijing seeks to expand its economic footprint in central and eastern Europe.
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