China's prison labour practices are in the spotlight after a six-year-old in Britain found a Christmas card saying it had been packed by foreign prisoners who were victims of forced labour in a Shanghai jail. 

China denied the allegations, saying the jail does not have an issue of foreign prisoners being forced to work. 

The manager of the printing factory where the card was made said the allegations were "completely fabricated."

Here is what Chinese law says about prison labour practices:

'COMBINING EDUCATION AND LABOUR'

China had 1.7 million people in 680 prisons as of 2018, said the director of prison administration under the Ministry of Justice, in an interview with the official Xinhua news agency in January last year. 

Labour is a part of the punishment process, according to the law. 

"Prisons will combine punishment and reform for criminals,with the principle of combining education and labour, to change criminals into law-abiding citizens," according to the prison law. 

Safeguards are in place, it says. 

According to the same law, prisoners usually work eight hours a day in manufacturing work.

If they must work beyond eight hours, they have to report to the head of the prison and receive his or her permission.

Sleeping time must not be less than eight hours, the same law says. 

In Shanghai, workers on average can receive up to 600 yuan ($85.57) a month for their work, according to the law. 

It is unclear which companies the prisoners supply. 

A report from state-backed Beijing News found that a Liaoning prison in China's northeast controlled businesses in near 20 different industries from cars to construction.

SHANGHAI QINGPU PRISON

The jail where the card is alleged to have come from is in Shanghai where prisoners with sentences of longer than seven years are kept. 

It also holds a number of male foreign prisoners from over 40 countries, according to its website. 

The prison "has also become a window to show China's civilised rule of law," the prison's website says.

LINKS TO COMPANIES

Supermarket chain Tesco suspended its relationship on Sunday with a Chinese supplier after news of the card's message alleging forced labour practices broke. 

Australian clothing retailer Cotton On Group said today it was investigating the same supplier. 

In 2014, Associated British Foods' fast-fashion chain Primark was criticised after a customer found a note inside a pair of trousers she bought that allegedly came from a Chinese prisoner who claimed to have been overworked. 

A Primark spokesperson said today it has 110 staff who keep tabs on suppliers and audit factories at least once a year to ensure that working conditions and pay meet standards based on international labour guidelines. 

In 2017, a customer found a handwritten note inside a Christmas card bought from Sainsbury supermarket group that apparently came from a Chinese prisoner. 

A spokesperson said the supermarket visits suppliers regularly to ensure they meet the company's ethical trading standards. 

It is unclear how many companies are supplied by Chineseforced prison labour. 

Another potential area of contention is the detention camps China has been running in Xinjiang province.

The Chinese government says they are vocational training centres. 

Using that term, the region has been wooing domestic companies to train and employ detainees, according to Adrian Zenz, an independent German researcher, who published his findings in Foreign Policy magazine.