A U.K. supermarket chain has apologized after halal-labeled products were discovered to contain pork blood and skin, prompting an outcry from Muslim customers this week. A man is pictured here walking past a shop selling halal meat in Australia. Reuters/David Gray

A supermarket chain in the United Kingdom apologized this week after selling products mislabeled as “halal,” or permissible for consumption by observant Muslims. The apology by the Germany-based Aldi supermarket followed an outcry by Muslim customers who discovered that a halal-labeled product stocked at the some of the chain's 500 stores contained pig blood and skin (pork is strictly forbidden in Islam).

“We have now investigated this matter with the supplier, who has advised that the packaging was incorrectly labeled as halal-certified and the problem is currently being rectified,” a spokesperson for Aldi said in a statement, reported by the Independent on Monday. “We apologize for any confusion caused by this unfortunate, isolated matter. While this is not a food safety or legal compliance issue, any customers who are not satisfied are welcome to return their purchase to store for a full refund.”

Angry customers had contacted the company after discovering that a product made by the Scottish company Punjab Pakora, a black pudding dish, was labeled "halal" but actually contained pork blood, skins and stock.

The owners of Punjab Pakora have attributed the labeling issue to human error, saying that “the mistake happened when we did the print run and unfortunately our manager failed to spot this error and got approval for printing,” the Independent reported. “We have been trying our very best and hardest [to correct the issue)] and have contacted different clients involved and have sorted the issue.”

Some customers expressed their outrage that neither company had noticed the mistake until the product was already on shelves. “This is absolutely outrageous and I am deeply offended by this,” one Muslim customer told the Daily Mail. “I am pretty sure many others of the Muslim community are also very offended by this. It is demoralizing and goes against religious morals and scripture.... and I speak on behalf of every Muslim and human that does not deserve to be misled by any sort of false claim of halal food or lies about what we consume.”

This is not the first U.K. scandal involving halal-labeled food and pork. In 2013, a company that supplied food to prisons was discovered to have traces of pork DNA in its halal-labeled products. The incident prompted an investigation by the country’s food standards agency. Under Islamic law, halal meat is defined as meat that is blessed while it is being slaughtered. Pork and any products derived from a pig are expressly forbidden.