Here are excerpts from the letter:
We respectfully decline to remove the Idaho Code and respectfully reject the distinction between “native” code and additional materials, as both are integral part and parcel of the only official Idaho Code, such material constituting the official laws of Idaho as published by the state. [...]
It is a long-held tenet of American law that there is no copyright in the law. This is because the law belongs to the people and in our system of democracy we have the right to read, know, and speak the laws by which we choose to govern ourselves. Requiring a license before allowing citizens to speak the law would be a violation of deeply-held principles in our system that the laws apply equally to all.
This principle was strongly set out by the U.S. Supreme Court under Chief Justice John Marshall when they stated “the Court is unanimously of opinion that no reporter has or can have any copyright in the written opinions delivered by this Court, and that the judges thereof cannot confer on any reporter any such right.” Wheaton v. Peters, 33 U.S. (8 Pet.) 591 (1834). The Supreme Court speciﬁcally extended that principle to state law, such as the Idaho Code, in Banks v. Manchester (128 U.S. 244, 1888) [...]
The distinction between “native” content (“the law”) and additional materials perhaps would have some bearing if the publication in question were the independent commercial endeavor of a publication ﬁrm. If such a ﬁrm were to copy the state statutes and compile that information with additional analyses and summaries and were to do so as a strictly commercial endeavor, we understand and respect that this material would be their private property.
However, the publication in question is not by some independent endeavor, it is by the Idaho Code Commission and the document is clearly labeled as the official Idaho Code. Your vendor states in its marketing materials that this document is “the only official source” for Idaho law. The Idaho Code is a publication of the State and it is the deﬁnitive statement by the State of the law. Any lawyer would ignore this publication any of its components at his or her peril. Any citizen wishing to read the Official Idaho Code would have trouble distinguishing between the material you outlined in red and those materials outside the box. No matter how you slice that cheese, it all looks the same. The Official Idaho Code, every component of it, is the law. [...]
For more details, please see the complete letter.