Colo. Rev. Stat. § 14-5-315
A party whose parentage of a child has been previously determined by or pursuant to law may not plead nonparentage as a defense to a proceeding under this article.
C.R.S. § 14-5-315
This section is similar to former § 14-5-128 as it existed prior to 1993.
COMMENT
Arguably this section does no more than restate the basic principle of res judicata. However, there is a great variety of state law regarding presumptions of parentage and available defenses after a prior determination of parentage. As long as a proceeding is brought in an appropriate forum, this section is intended neither to discourage nor encourage collateral attacks in situations in which the law of another jurisdiction is at significant odds with local law. If a collateral attack on a parentage decree is permissible under the law of the issuing jurisdiction, such a proceeding must be pursued in that forum and not in a UIFSA proceeding.
This section mandates that a parentage decree rendered by another tribunal "pursuant to law" is not subject to collateral attack in a UIFSA proceeding. Of course, an attack on an alleged final order based on a fundamental constitutional defect in the parentage decree is permissible in the forum state. For example, a responding tribunal may find that another tribunal acted unconstitutionally by denying a party due process due to a failure of notice and opportunity to be heard or a lack of personal jurisdiction over a party who did not answer or appear. Insofar as the latter ground is concerned, the universal enactment of the long-arm statute asserting personal jurisdiction over a respondent if the child "may have been conceived" in the forum state may greatly reduce successful attacks on a parentage determination. See Section 201(a)(6).
Similarly, the law of the issuing state or foreign country may provide for a determination of parentage based on certain specific acts of the obligor, such as voluntarily acknowledging parentage as a substitute for a decree. UIFSA also is neutral regarding a collateral attack on such a parentage determination filed in the issuing tribunal. In the meantime, however, the responding tribunal must give effect to such an act of acknowledgment of parentage if it is recognized as determinative in the issuing state or foreign country. The consistent theme is that a collateral attack on a parentage determination cannot be made in a UIFSA proceeding other than on fundamental due-process grounds.