I can't say if there is a NEC article (because I'm too lazy to look), but it may be covered by city codes. Many services and panelboard "walls" I have done - in NJ - have been mounted on wood with fire proof paint (black). It's gotten to the point I don't ask if it's required, I just do it. Some supply houses here have actually started carring fire-proofed plywood cut into a 2'x4' sheet
~~ CELTIC ~~
...-= NJ =-...