Be ye not unequally yoked together with unbelievers.
This verse is often used in connection with marriage. But you can apply it to every decision in life. If you establish any kind of relationship with an unbeliever you are going against this advice by the Apostle. Be careful. A yoke is often binding and hard, sometimes impossible, to break. Permanent associations with unbelievers can lead to having to support decisions that are against the Lord. Be careful with whom you associate.