A 6-year-old girl in London preparing Christmas cards for her classmates found a message said to be from prisoners forced into labor in China, prompting the Tesco grocery chain to suspend ties with a supplier.

Florence Widdicombe was going through cards her mother purchased about a week ago at a Tesco supermarket when she saw one card had writing in it, her father, Ben Widdicombe, told the BBC.

“We are foreign prisoners in Shanghai Qingpu Prison China,” the handwritten note read. “Forced to work against our will. Please help us and notify human rights organization.”

The New York Times could not independently authenticate the note, which also suggested that the recipient contact Peter Humphrey, a British journalist who was a prisoner at Qingpu from 2013 to 2015. Mr. Humphrey, who was jailed on corruption charges he says were bogus while working as a fraud investigator, first wrote about the note in The Sunday Times.