Ethnically, yes, this would be immoral. On the basis of nationality, it's absolutely not immoral. In fact, in the US, it's /required by law/ to discriminate in this way if your company works on technology related to national security. It is illegal to discriminate on the basis of national origin, someone's birthplace, but not on the basis of nationality, their citizenship, in the case of national security. Only US citizens, including those who are naturalized, may work on technology related to national security within the US.

What is prudent is another matter besides that which is legal. That which is moral is another matter besides that which is legal. I've made my opinion known, you're welcome to form your own.