BERLIN (Reuters) - European fashion giants H&M HMb.ST and C&A, as well as technology company 3M MMM.N, are looking into a report in the Financial Times alleging that inmates of a Chinese prison made packaging used by the companies.

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C&A’s chief sustainability officer Jeffrey Hogue said the privately-held company owned by Swiss-based Cofra Holding AG took the allegations very seriously and was investigating.

“We have a zero tolerance policy for any form of modern slavery including forced, bonded or prison labor. If we detect a case, we immediately terminate our relationship with the supplier,” Hogue said in an emailed statement.

Peter Humphrey, a British corporate investigator and former journalist, spent 23 months in jail in China for allegedly obtaining private records of Chinese citizens and selling the information on to clients including drugmaker GlaxoSmithKline Plc, charges he has denied.

In an article for the Financial Times last week, Humphrey described his time in jail, including work the prisoners did: “Our men made packaging parts. I recognized well-known brands - 3M, C&A, H&M.”

The article also made mention of prisoners making textiles and components, but did not say for whom.

An H&M spokeswoman said the Swedish company was looking into the allegations, but could not yet say whether they were true.

Companies have been making more robust efforts to ensure their supply chains are clean of trafficking and forced labor, but there is still room for improvement, according to an annual index compiled by EcoVadis.

“It is completely unacceptable placing manufacturing into prisons and it seriously violates the regulatory framework that our suppliers must follow,” the H&M spokeswoman said.

“A failure to comply would immediately lead to permanent termination of our business contract.”

3M, which also has policies prohibiting the use of forced labor, also said it was investigating the report.

“3M does not engage or participate in exploitative working conditions, and we are not aware of any 3M suppliers in China using prison labor,” a spokesman said.