China has been accused of committing crimes against humanity against the Uyghur population and other mostly-Muslim ethnic groups in the north-western region of Xinjiang.
In state-sponsored programmes, detainees are forced to produce goods including polysilicon, a core ingredient in solar panels, according to the US Department of Labor.
The Chinese government has denied all allegations of human rights abuses in Xinjiang.
Longi and Aiko are both members of the Solar Stewardship Initiative, which is a scheme designed to develop confidence in the supply chain and the responsible sourcing of solar panels.
An Aiko spokesperson said the company was “committed to upholding the highest standards of ethical business conduct and responsible sourcing”.
“We take any concerns related to human rights and labour practices seriously and expect our suppliers to do the same,” the spokesperson said.
“As part of our ongoing efforts, we engage with suppliers to promote transparency and continuous improvement in line with international guidelines. We are also closely monitoring global supply chain developments and remain committed to working with stakeholders to support a fair and sustainable solar industry.”
Longi said it regretted the findings of the Sheffield Hallam University report and “categorically affirms that forced labour has no place within our supply chain”.
A company spokesperson said the conclusions in the Over-Exposed report “may not fully reflect the comprehensive measures Longi has implemented to ensure full compliance with international labour standards”.
“Independent third-party audits play a critical role in verifying compliance and identifying potential risks,” the spokesperson said.
“While the complexity of global supply chains presents challenges, Longi remains steadfast in its efforts to eliminate any risks associated with forced labour.”