Colorado constitution
Article V
Section 40

If any person elected to either house of the general assembly shall offer or promise to give his vote or influence in favor of or against any measure or proposition pending or proposed to be introduced in the general assembly in consideration or upon condition that any other person elected to the same general assembly will give or will promise or assent to give his vote or influence in favor of or against any other measure or proposition pending or proposed to be introduced in such general assembly, the person making such offer or promise, shall be deemed guilty of solicitation of bribery. If any member of the general assembly shall give his vote or influence for or against any measure or proposition pending in such general assembly, or offer, promise or assent so to do, upon condition that any other member will give or will promise or assent to give his vote or influence in favor of or against any other measure or proposition pending or proposed to be introduced in such general assembly, or in consideration that any other member hath given his vote or influence for or against any other measure or proposition in such general assembly, he shall be deemed guilty of bribery; and any member of the general assembly, or person elected thereto, who shall be guilty of either of such offenses shall be expelled, and shall not be thereafter eligible to the same general assembly; and, on conviction thereof in the civil courts, shall be liable to such further penalty as may be prescribed by law.