IMO, a Christian knowingly eating halal meat may be disobeying the instruction in Acts 15 against eating things sacrificed to idols.
Exactly what I was thinking. Acts 15:23-29
With them they sent the following letter: The apostles and elders, your brothers, To the Gentile believers in Antioch, Syria and Cilicia: Greetings. We have heard that some went out from us without our authorization and disturbed you, troubling your minds by what they said. So we all agreed to choose some men and send them to you with our dear friends Barnabas and Paul—men who have risked their lives for the name of our Lord Jesus Christ. Therefore we are sending Judas and Silas to confirm by word of mouth what we are writing. It seemed good to the Holy Spirit and to us not to burden you with anything beyond the following requirements: You are to abstain from food sacrificed to idols, from blood, from the meat of strangled animals and from sexual immorality. You will do well to avoid these things. Farewell.
Acts 21:25
As for the Gentile believers, we have written to them our decision that they should abstain from food sacrificed to idols, from blood, from the meat of strangled animals and from sexual immorality.
And Finally Revelation 2:12-20
To the angel of the church in Pergamum write: These are the words of him who has the sharp, double-edged sword. I know where you live—where Satan has his throne. Yet you remain true to my name. You did not renounce your faith in me, even in the days of Antipas, my faithful witness, who was put to death in your city—where Satan lives. Nevertheless, I have a few things against you: You have people there who hold to the teaching of Balaam, who taught Balak to entice the Israelites to sin by eating food sacrificed to idols and by committing sexual immorality. Likewise you also have those who hold to the teaching of the Nicolaitans. Repent therefore! Otherwise, I will soon come to you and will fight against them with the sword of my mouth. He who has an ear, let him hear what the Spirit says to the churches. To him who overcomes, I will give some of the hidden manna. I will also give him a white stone with a new name written on it, known only to him who receives it.
To the angel of the church in Thyatira write: These are the words of the Son of God, whose eyes are like blazing fire and whose feet are like burnished bronze. I know your deeds, your love and faith, your service and perseverance, and that you are now doing more than you did at first. Nevertheless, I have this against you: You tolerate that woman Jezebel, who calls herself a prophetess. By her teaching she misleads my servants into sexual immorality and the eating of food sacrificed to idols.
But 1 Cor. 8 says
So then, about eating food sacrificed to idols: We know that an idol is nothing at all in the world and that there is no God but one. For even if there are so-called gods, whether in heaven or on earth (as indeed there are many "gods" and many "lords"), yet for us there is but one God, the Father, from whom all things came and for whom we live; and there is but one Lord, Jesus Christ, through whom all things came and through whom we live.There is an argument for not having the option, but as long as the Christian does not believe that there are any other gods, and that the meat couldn't really be sacrificed to the idol because the idol is a figment of some peoples' imaginations, then there is no problem. That said, why should the government support one strict interpretation of Islam over a strict interpretation of Christianity--especially since Christianity is much more common?
But not everyone knows this. Some people are still so accustomed to idols that when they eat such food they think of it as having been sacrificed to an idol, and since their conscience is weak, it is defiled. But food does not bring us near to God; we are no worse if we do not eat, and no better if we do.
Be careful, however, that the exercise of your freedom does not become a stumbling block to the weak. For if anyone with a weak conscience sees you who have this knowledge eating in an idol's temple, won't he be emboldened to eat what has been sacrificed to idols? So this weak brother, for whom Christ died, is destroyed by your knowledge. When you sin against your brothers in this way and wound their weak conscience, you sin against Christ. Therefore, if what I eat causes my brother to fall into sin, I will never eat meat again, so that I will not cause him to fall.