While referencing Scripture on a different subject I ran across the following in the Book of Mark. I interpreted Mark's recollection of Jesus' words as support for demanding lawful money, not accepting or endorsing federal reserve notes.

Mark 12
[14] And when they were come, they say unto him, Master, we know that thou art true, and carest for no man: for thou regardest not the person of men, but teachest the way of God in truth: Is it lawful to give tribute to Caesar, or not?
[15] Shall we give, or shall we not give? But he, knowing their hypocrisy, said unto them, Why tempt ye me? bring me a penny, that I may see it.
[16] And they brought it. And he saith unto them, Whose is this image and superscription? And they said unto him, Caesar's.
[17] And Jesus answering said unto them, Render to Caesar the things that are Caesar's, and to God the things that are God's. And they marvelled at him.