JOHANNESBURG, South Africa – A new report documenting dangerous working conditions and other labor abuses at Chinese-owned copper mines in Zambia challenges recently elected President Michael Sata to act on a key campaign promise: holding Chinese investors accountable.

In interviews conducted by the New York-based group Human Rights Watch, Zambian workers recounted working 12 and even 18-hour shifts at Chinese mines, sometimes in extreme heat and contact with noxious chemicals. If workers refused to work in unsafe conditions, or tried to organize into unions, they faced being fired, according to the report released Thursday.

Copper is the mainstay of Zambia’s economy, and China is the country’s biggest foreign investor, with $2 billion invested in copper, cobalt, nickel and coal mines. Zambia has seen strong economic growth, averaging 6 percent over the last three years.

But in Zambia, and across Africa, Chinese employers have a reputation for low pay and poor working conditions, sparking protests by local staff and sometimes even violence.

President Sata has previously taken a populist, outspoken stance critical of Chinese investment in Zambia, referring to Chinese investors as “infesters” and accusing Chinese companies of using “slave labor.”

But in his election campaign this year, and since becoming president in September, he appears to have softened his views, saying that the Chinese are welcome if they follow Zambian laws. Just last weekend, Sata hosted a lunch for Chinese investors at his official residence, the State House, in Lusaka.

"Foreign investment is important to Zambia and we will continue to work with foreign investors who are welcome in the country ... but they need to adhere to the labor laws," Sata declared shortly after being sworn in as president.

More from GlobalPost: Zambian election results check Chinese influence in Africa

The Human Rights Watch report is based on more than 170 interviews, including 95 with workers at four Chinese state-run copper mines, all subsidiaries of China Non-Ferrous Metals Mining Corporation.

“Sometimes when you find yourself in a dangerous position, they tell you to go ahead with the work,” one miner, who works for Non-Ferrous China Africa, told researchers. “They just consider production, not safety. If someone dies, he can be replaced tomorrow. And if you report the problem, you’ll lose your job.”

Researchers note that while there have been improvements on some labor issues since Chinese companies began operating in Zambia in 2003, “they still fail to meet the standards of both labor law and their multinational competitors in Zambia’s copper industry.”

The report also points out that many of the poor health and safety practices found at Chinese-run mines in Zambia were similar to the labor abuses commonly seen in China.

Human Rights Watch called on Sata to “act on his campaign promises to end the abuse and improve government regulation of the mining industry to ensure that all companies respect Zambia’s labor laws.”

“Rather than simply blame Chinese-run firms, President Sata needs to ensure that his government is effectively protecting workers’ rights,” said Daniel Bekele, the organization’s Africa director. “More stringent measures are needed against all companies that flout labor laws and mining regulations.”

In response to the report, China Non-Ferrous Metals Mining Corporation, which is under control of the State Council — China’s Cabinet — issued a lengthy letter explaining its policies and promising an in-depth investigation.

More: Sata wins in Zambia poll upset

“We will remain open-minded and serious, and pay attention to all the valuable opinions from people from all walks of life,” the letter said. “If you are able to witness some of the improvements made in our enterprises in the near future, that shall be of greatest comfort to us.”

With regards to workers’ concerns about being coerced into dangerous work at the Non-Ferrous China Africa mine, the letter said that “language and cultural differences during communication and interaction with workers, as well as during work planning, could have possibly resulted in misunderstandings about the actual state of affairs.”

A previous report on labor practices at Chinese companies in Africa similarly found that many firms violate basic workplace safety rules and pay their local staff below the legal minimum wages.

The African Labour Research Network report from 2009 included 10 African countries, and said that in Zambia, while Chinese companies had official policy statements on workplace health and safety, the policies were not being followed.

“A number of workers in Chinese companies interviewed at [Non-Ferrous China Africa] Mining and China Geo-Engineering Corporation felt that Chinese companies paid lip service to occupational health and safety issues,” the report said, adding that, “The seriousness with which Chinese companies adhere to health and safety is doubtful.”

Related: China invests in Zambia copper mines (VIDEO)

Erin Conway-Smith is GlobalPost's South Africa correspondent. Follow her on Twitter: Follow @ejcs