I don’t see how it would be a problem in general. However, there are different circumstances which change the answer to that question. Let’s say you’re working for a company that makes the parts for nuclear bombs. To me, that would be immoral because the Church clearly condemns nuclear weaponry because they are weapons of mass destruction.
[quote=Catechism of the Catholic Church]**2314 **“Every act of war directed to the indiscriminate destruction of whole cities or vast areas with their inhabitants is a crime against God and man, which merits firm and unequivocal condemnation.” A danger of modern warfare is that it provides the opportunity to those who possess modern scientific weapons especially atomic, biological, or chemical weapons - to commit such crimes.
On the other hand, if you’re working for a company that makes MREs (meals ready to eat) for soldiers on the field, I see no conflict between my faith and that.
But let’s say you work for a company that makes the weapons used in the battles and such. Would that be immoral? I honestly don’t know. I guess it depends on if you know where these weapons are going. In other words, if you know what front they are going to. Say they are going to the Iraq war. To me, my conscience would not allow me to work for a company producing weapons for an unjust war. But say the weapons are going to a different place where the war is just. I would not have a conflict with my conscience and my faith in the last situation.