Eating meat killed in a ritualistic manner (Kutha meat): Sikhs are strictly prohibited from eating meat killed in a ritualistic manner (such as halal or kosher, known as Kutha meat ), or any meat where langar is served.
Sikhs and Sikhism, Dr. I.J.Singh, Manohar Publishers.
And one semitic practice clearly rejected in the Sikh code of conduct is eating flesh of an animal cooked in ritualistic manner; this would mean kosher and halal meat. The reason again does not lie in religious tenet but in the view that killing an animal with a prayer is not going to enoble the flesh. No ritual, whoever conducts it, is going to do any good either to the animal or to the diner. Let man do what he must to assuage his hunger. If what he gets, he puts to good use and shares with the needy, then it is well used and well spent, otherwise not.