Under Islamic law, Muslims are not allowed to eat pork.
They can only eat Halal meat - which is prepared in a certain way.
But tests found pies and pasties described as Halal had traces of pork DNA.
The Ministry of Justice said it had withdrawn the products immediately, while the Justice Minister Jeremy Wright said the Prison Service was investigating "as a matter of urgency".
It comes after traces of horsemeat were found in burgers sold by some UK supermarkets, including Tesco.
"All prisons have been informed about this very regrettable incident and we reported this issue to the Food Standards Agency immediately," a spokesman for the Ministry of Justice said.
"We are taking immediate steps to suspend the contract with the relevant sub-contractor."
Mr Wright said: "This is an absolutely unacceptable situation and one which we regret greatly.
"This must be distressing for those affected and they can be reassured we are doing everything we can to resolve the situation. The Prison Service is investigating this as a matter of urgency."
The company involved has not been named and it is not known where the firm is based.
They can only eat Halal meat - which is prepared in a certain way.
But tests found pies and pasties described as Halal had traces of pork DNA.
The Ministry of Justice said it had withdrawn the products immediately, while the Justice Minister Jeremy Wright said the Prison Service was investigating "as a matter of urgency".
It comes after traces of horsemeat were found in burgers sold by some UK supermarkets, including Tesco.
"All prisons have been informed about this very regrettable incident and we reported this issue to the Food Standards Agency immediately," a spokesman for the Ministry of Justice said.
"We are taking immediate steps to suspend the contract with the relevant sub-contractor."
Mr Wright said: "This is an absolutely unacceptable situation and one which we regret greatly.
"This must be distressing for those affected and they can be reassured we are doing everything we can to resolve the situation. The Prison Service is investigating this as a matter of urgency."
The company involved has not been named and it is not known where the firm is based.
