The view of Sikhism is that eating meat or abstaining from it is the individuals choice. A Sikh is considered no lesser or greater a Sikh if they eat meat or are a vegetarian.

The Akal Takht represents the final authority on controversial issues concerning the Sikh Panth, in this regard the issue of meat eating has been settled. Hukamnama issued by Akal Takht Jathedar Sandhu Singh Bhaura dated February 15th 1980 that Amritdhari Sikhs can eat meat as long as it is jhatka meat and that eating meat does not go against the code of conduct, Kurehit, of the Sikhs. Thus a Sikh cannot be excommunicated for eating meat.

The Times of the Gurus

The Bani of Guru Nanak on Meat and Vegetarianism

Quotes from Sri Guru Granth Sahib

The Comments of Sikh Scholars Regarding Meat

An Amritdhari Khalsa Sikh is not allowed to eat the meat of an animal slaughtered the Muslim way.

In Punjabi the word "Kuttha" specifically means meat prepared according to the Muslim ritual slaughter.

Punjabi-English Dictionary, Punjabi University, Dept. of Punjabi Lexicography, Published Dec. 1994. "Kuttha: meat of animal or fowl slaughtered slowly as prescribed by Islamic law."

Punjabi English Dictionary, Singh Bros., Amritsar "Kuttha: Tortured, killed according to Mohammedan law."

Jhatka meat is meat in which the animal has been killed quickly without suffering or religious ritual.

Sikhism, A Complete Introduction, Dr. H.S.Singha & Satwant Kaur, Hemkunt Press
We must give the rationale behind prescribing jhatka meat as the approved food for the Sikhs. According to the ancient Aryan Hindu tradition, only such meat as is obtained from an animal which is killed with one stroke of the weapon causing instantaneous death is fit for human consumption. However, with the coming of Islam into India and the Muslim political hegemony, it became a state policy not to permit slaughter of animals for food, in any other manner, except as laid down in the Quran - the kosher meat prepared by slowly severing the main blood artery of the throat of the animal while reciting verses from the Quran. It is done to make slaughter a sacrifice to God and to expiate the sins of the slaughter. Guru Gobind Singh took a rather serious view of this aspect of the whole matter. He, therefore, while permitting flesh to be taken as food repudiated the whole theory of this expiatory sacrifice and the right of ruling Muslims to impose iton the non-Muslims. Accordingly, he made jhatka meat obligatory for those Sikhs who may be interested in taking meat as a part of their food.

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.

The reason why meat is not served at langar in the Gurdwaras is because langar is supposed to be a symbol of equality of mankind where all people no matter what race, religion or caste can eat toghether in the atmosphere of brotherhood. Hindu, Sikh, Muslim, it does not matter who they are. Different religions have different dietary restrictions. Hindus cannot eat cow, muslims cannot eat pork and will only eat halal meat. Jews will only eat kosher meat, others cannot eat fish or eggs. But in a gurdwara langar, it does not matter what their dietary taboos or religious beliefs are, the food is designed so that all can eat together and no one will be offended or not be able to partake of the meal.