If they are eating meat slaughtered by Christians or Jews (referred to as the People of the Book in the Qur’an), you cannot object to them; although it would be best that they go for meat slaughtered by Muslims if it is readily available.

For further details on this, let me cite here one of my earlier answers:

“The question of meat slaughtered by the People of the Book has been a controversial issue among Muslim scholars. The vast majority of scholars from all of the four schools consider it permissible for us. They base this on the clear statement of the Qur’an: “Today, I have permitted for you all good things, and the food of the People of the Book is permissible for you, and your food is permissible for them.” (Al-Ma’idah: 5)

According to Ibn `Abbas, the food of the People of the Book mentioned in the above verse refers to the meat slaughtered by them.

Based on this, the majority of scholars belonging to the four schools of thought consider it permissible for Muslims to eat animals slaughtered by the Christians and Jews so long as these animals are considered lawful for us to eat.

If you fall in this category of those who live among the People of the Book, then you may eat their meat, especially if you cannot find meat slaughtered by Muslims.

As for stunning the animal, it does not make the animal dead, for it is intended only to knock the animal unconscious so that it does not feel pain and it is brought under control. This itself does not render the animal impure and unlawful unless it is dead before slaughter.

My own experience with the slaughterhouses is that they do not make use of animals that are already dead before slaughter. Inspectors, who are appointed by the government (in countries such as Canada), do make sure that this is not the case.

As far as the wisdom of stunning is concerned, it is really in conformity with the wisdom established in the Prophetic hadith in which the Prophet (peace and blessings be upon him) is reported to have said, “Allah has prescribed excellence and compassion in all things, so when you kill, kill well; when you slaughter, slaughter well, and let him sharpen his knife and spare the animal pain.”

In conclusion, we are definitely allowed to partake of such meat, especially if we do not find meat provided by Muslims.”