Fast food giant Subway has removed ham and bacon from almost 200 outlets, and switched to halal meat alternatives in an attempt to please its Muslim customers.
It has confirmed turkey ham and turkey rashers will be used instead in 185 of its stores, where all the meat will now be prepared according to halal rules.
The chain, which has around 1,500 outlets across the UK, explained its decision by saying it had to balance animal welfare concerns with 'the views of religious communities'.
Traditional halal slaughter sees animals have their throats slit before bleeding to death. But Subway stressed that the meat served in its sandwiches would come from animals that have been stunned first, a practice that aims to reduce any suffering.
In Arabic the word halal means 'permitted' or 'lawful' and defines anything that is allowed or lawful according to the Qur'an.
It is often used to indicate food - particularly meat - has been prepared in accordance with Muslim principles and techniques.
Muslims are forbidden from eating any non-halal food and meat from pigs and Subway said customers can identify those stores selling halal food by the special 'All meats are Halal' sign, which must be displayed in participating branches.
In the halal-only branches ham and bacon has been substituted for turkey ham and rashers.
Many animal charities condemn halal slaughter as being cruel to animals.
Traditionally in halal abattoirs the throats of the animals are cut while they are fully conscious - an act many campaigners say is inhumane and needlessly cruel.
In non-halal abattoirs, livestock are stunned before killing to prevent any unnecessary suffering.
Some halal butchers also practise pre-stunning, though it is not permitted by some Islamic scholars.
In Britain, killing an animal without prior stunning is illegal, but the law gives special exemption to Muslim and Jewish meat producers on the grounds of religion.
There are thought to be around 12 abattoirs dedicated to unstunned slaughter in the UK, while hundreds practise stunned halal slaughter.
A Subway spokeswoman told MailOnline all halal meat served in the participating branches is from animals who were stunned prior to slaughter.
She said: 'The growing popularity of the Subway chain with the diverse multicultural population across the UK and Ireland means we have to balance the values of many religious communities with the overall aim of improving the health and welfare standards of animals.
'We put a programme into place in 2007 to ensure that the population demographic is taken into account when new store openings are considered in order that we meet consumer demand in each location.
All ham and bacon is replaced by turkey ham and turkey rashers and all meat is prepared according to Islamic halal rules.
'All our suppliers comply with EU animal welfare legislation as a minimum and we require suppliers of halal products to adopt the stunning of animals prior to their slaughter.
'All halal meats are certified by the appropriate halal authorities.
'All halal Subway stores have numerous signs stating that they serve halal food.
'These are situated on the menu panels, nutritional information and in the front window of the store.'
Animal campaigning charity PETA urged people to opt for a vegetarian diet to ensure they have the best interests of animals at heart.
A spokesman said: 'At the best of times, meat is a product of a bloody and violent industry with no respect for other living beings who value their lives in the same way that we do and experience the same pain and terror that Subways' customers would if they were killed for a sandwich.
'Most religions, including Islam, preach kindness to animals, but words are one thing and practice another.
'As the Dalai Lama said, "My religion is kindness". And a diet that expresses kindness, is open to all religions and truly respects animal rights is a vegan one.
'Subway-goers, no matter what their religion, can eat with a clear conscience by opting for the veggie patty, the veggie delight or, heaven forbid, a salad.'
Speaking about the general issue of halal slaughter, an RSPCA spokeswoman added: 'Scientific research has clearly shown that slaughter of an animal without stunning can cause unnecessary suffering, and the RSPCA is opposed to the slaughter of any animal without first making it insensible to pain and distress.
'At present, the only legal exemptions to stunning during slaughter exist for kosher and halal methods of slaughter, however, it is important to differentiate between ‘religious’ and ‘non-stun’ slaughter as around 90 per cent of all halal in the UK receives a stun before slaughter.
'Our concern has nothing to do with the expression of religious belief but with the practice of killing by throat cutting without pre-stunning.
'We believe that meat produced from animals stunned or not stunned before slaughter should be clearly labelled to allow consumer choice, and continue to press for changes in the law that would improve the welfare of all farm animals at the time of slaughter.'
Halal refers to any object or action which is permissible according to Islamic law. The term covers not only food and drink but also matters of daily life.
Halal foods are those that Muslims are allowed to eat or drink under Islamic Shari'ah. The criteria dictates both food which are allowed and how the food must be prepared. The foods most commonly addressed are types of meat and animal tissue.
The most common example of non-halal, or forbidden food is pork. It is the only meat that must not be eaten by Muslims at all, due to historical, cultural and religiously perceived hygienic concerns.
Other meats can be forbidden, depending on their source, the cause of the animal's death and how it was processed.
To be halal, the food must have come from a supplier that uses halal practises. Specifically the slaughter must be performed by a Muslim, who must invoke the name of Allah prior to killing the animal. Commonly a person will say 'Bismillah' ('In the name of God') before repeating 'Allahu akbar' ('God is the greatest') three times.
The animal is then slaughtered with a sharp knife, by cutting the throat, windpipe and blood vessels in the neck without cutting the spinal cord. The blood must then be drained from the veins of the animal.
Traditionally and according to Islamic scholars an animal must be conscious while slaughtered.
However the majority of halal abattoirs stun the animals before killing them.
Muslims must also ensure that all foods, particularly processed foods, as well as non-food items like cosmetics and pharmaceuticals, are halal.