Colo. Rev. Stat. § 8-70-130
"Employment" does not include services performed in the employ of the United States government, a national bank or state bank that is a member of the federal reserve system, or a federal savings and loan association or a state building and loan association that is a member of the federal home loan bank system, which institutions were, prior to January 1, 1972, exempt from articles 70 to 82 of this title, or any other instrumentality of the United States exempt under the constitution of the United States from the premiums imposed by articles 70 to 82 of this title; except that, to the extent that the congress of the United States permits states to require any instrumentalities of the United States to make payments into an unemployment fund under a state unemployment compensation law, all of the provisions of articles 70 to 82 of this title shall be applicable to such instrumentalities and to services performed for such instrumentalities in the same manner, to the same extent, and on the same terms as to all other employers, employing units, individuals, and services. If this state is not certified for any year by the United States secretary of labor under section 3304 of the federal "Internal Revenue Code of 1986", as amended, the payments required of such instrumentalities with respect to such year shall be refunded by the division from the fund in the same manner and within the same period as is provided in section 8-79-108 with respect to premiums erroneously collected.
C.R.S. § 8-70-130