Let me tell you first what you should not do: You should not give in to your boss's demand that you do something wrong. If it's illegal, you could be opening yourself up to charges later on -- but beyond that, if you gave in you would be compromising your faith and doing something that will bring dishonor to Christ.
Admittedly you are facing a difficult situation. But God knows all about it, and He will not abandon you. He can be trusted -- and that's what I encourage you to do: Trust Him in the days ahead. Pray for your boss, and pray that God will give you both courage and grace as you deal with him. God's promise is for you: "I was young and now I am old, yet I have never seen the righteous forsaken or their children begging bread" (Psalm 37:25).
Explain to him -- calmly but clearly -- that while you respect him and want to be the best employee you can be, you cannot do what he's asking you to do in this situation. Not only is it wrong, you should say, but you also firmly believe that in the long run both he and your company will be hurt.
He may not agree; he may even find an excuse to fire you. But God is faithful, and He can be trusted to open new doors for you. The Bible says, "The Lord rewards every man for his righteousness and faithfulness" (1 Samuel 26:23).