Colorado constitution
Article XXIV
Section 5

The excise tax on sales at retail, together with all license fees levied by article 26 of title 39, Colorado Revised Statutes, and amendments thereto, are hereby continued in full force and effect beyond the date on which said taxes and license fees would otherwise expire, and shall continue until repealed or amended; provided, however, that no law providing revenue for the old age pension fund shall be repealed, nor shall any such law be amended so as to reduce the revenue provided for the old age pension fund, except in the event that at the time of such repeal or amendment, revenue is provided for the old age pension fund in an amount at least equal to that provided by the measure amended or repealed during the calendar year immediately preceding the proposed amendment or repeal.