If you have not done so already, we always suggest contacting the nonprofit's Board Chair and/or Board of Directors. You can typically find the organization's Board Chair on their website or Form 990.
If the board fails to resolve or address the issue, you may contact the below agency to file a complaint:
For complaints regarding a nonprofit in non-compliance with the Internal Revenue Code (e.g. nonprofit refused to disclose tax forms upon request).
For complaints regarding violations of the Colorado Charitable Solicitations Act file with both the AG and Secretary of State's offices.
BBB works with the Colorado Attorney General on complaints againts companies.