When six-year-old Florence Widdicombe was writing Christmas cards to her friends, she found that one of the cards contained a message. The note in the Christmas charity card from Tesco read, “We are foreign prisoners in Shanghai Qingpu prison China. Forced to work against our will. Please help us and notify human rights organization.” The message also urged the reader to contact Peter Humphrey, a former British journalist who spent two years in the Qingpu prison because of unreasonable convictions.

At first, the Widdicombes, a family from south London, found the plead questionable, believing it was a prank. Upon further thought, Mr. Widdicombe decided to contact Mr. Humphrey, the name mentioned in the message. The former journalist took the story to the Sunday Times. He thinks the appeal for help was written as a collective message from his old cellmates. Mr. Humphrey also claims to know the identity of the transcriber but refuses to disclose a name.

The Qingpu prison is located on the outskirts of Shanghai, 100 kilometres away from the Zheijiang Yunguang Printing factory, where the cards are produced. Mr. Humphrey described the harsh conditions that he encountered at the prison but mentioned that, during his imprisonment, labour was optional and could be done in exchange for low wages. However, the message is evidence that labour in Qingpu prison is now obligatory.

Tesco is reportedly “shocked” by the incident and has since removed the cards from store shelves. Revenue from the Christmas charity cards raises £300,000 a year for the British Heart Foundation, Cancer Research U.K. and Diabetes U.K.. But, the grocery retailer has ceased production of the cards, while it opens an investigation into the factory.

Mr. Humphrey said that it would have been impossible for Tesco to know if the factory was subcontracting labour to the Qingpu prison, as auditors are prohibited from entering prisons. In Humphrey’s article for the Sunday Times, he wrote, “The daunting reality is that China’s prisons are closed to independent auditors who have little chance of unravelling the secretive business arrangements that have turned the jail system into a lucrative profit centre for the Chinese state.”

But this is hardly an isolated incident. In 2014, a woman from Northern Ireland found a similar note on a pair of Primark Trousers. Sent from China’s Xiangnan prison, it detailed the long working hours that prisoners are forced to endure under penal labour. As well as the poor quality of the prison’s food, it read, “What we eat is even worse than food for pigs and dogs.” Two years ago, a woman from Essex found a message in a Christmas card stating, “Wishing you luck and happiness. Third Product Shop, Guangzhou Prison, Number 6 District.”

Mr. Humphrey noted that other companies could be culprits, knowingly or unknowingly, in exploiting prison labour in China. While in Qingpu prison, he saw the names of many Western clothing brands and other well-known retailers on products being made by prisoners.

The United Nations’ manual on Human Rights and Prisons, as well as its Standard Minimum Rules for the Treatment of Prisoners, present clear regulations pertaining to prison labour. The former affirms that forced or compulsory labour is strictly prohibited and that “work of prisoners should not be subordinated merely to making a profit…for a private contractor.” The latter upholds the necessity of equitable remuneration and non-afflictive labour within prisons. The contents of these documents must be implemented throughout penal institutions to end the violation of prisoners’ rights.