The couple adopted a girl in New Jersey in 2006, obtaining a court ruling that gave them full rights as parents, the weekly Mladina and the daily Delo reported today.
They wanted to make the adoption legal in Slovenia and received approval from the Ljubljana District Court, becoming the first gay couple in Slovenia to get the same rights as biological or adoptive parents.
However, the State Prosecutor General lodged a request for protection of legality, arguing that recognising the verdict of the US court jeopardised the legal and moral integrity of Slovenian law.
The Supreme Court rejected the appeal, saying that Slovenian law as well as the laws of the European Union and the Council of Europe needed to be taken into consideration, a concept known as "international public policy".
This means, the court said, that Slovenian courts cannot reject verdicts of foreign courts even if they run contrary to Slovenian public policy, as long as such verdicts are in accordance with international public policy.
The Supreme Court verdict had also been mentioned by Labour, Family and Social Affairs Minister Ivan Svetlik during Monday's debate in parliament about the proposed new family law.
"This is a precedent that can be used any time for any such case," Svetlik is quoted as saying by Mladina.
The family law has been embroiled in a veritable culture war along liberal-conservative lines, with opponents of gay adoptions arguing that this undermined the traditional heterosexual family.
The bill was endorsed in the first reading in parliament, but conservative groups have already said it would be put to referendum if it is passed.