So going back to the original question and paraphrasing it "which is more important - union or constitution" and thinking of ONLY those two words...
union- [A combination so formed, especially an alliance or confederation of people, parties, or political entities for mutual interest or benefit.]
constitution- [The system of fundamental laws and principles that prescribes the nature, functions, and limits of a government or another institution.]
I say a union is more important than a constitution because it gives strong protection to any group. A constitution may or may not apply to a group and only applies to organization.
But my answer could change if I had a better question with MORE contex.