The judge added that "the objective of protecting the traditional family can not justify discrimination on grounds of sexual orientation" and that "the concept of "spouse" within the meaning of the directive also includes spouses of the same sex".
The term "spouse" includes same-sex partners under European Union law, meaning that member states can not deny them residence rights even if gay marriage is illegal in that country, the legal advisor to the bloc's top court said Thursday.
However, the Romanian authorities refused to grant Mr Hamilton that right of residence on the ground, inter alia, that he could not be classified in Romania as the "spouse" of an European Union citizen, that member state not recognising same-sex marriage.
Wathelet issued the opinion in regards to a 2010 case involving a Romanian citizen named Adrian Coman who married his American husband, Claibourn Robert Hamilton, in Brussels in 2010.
Romania has laws that prohibit the marriage of same sex couples, and doesn't recognise them at all in the legal system - resulting in the Romanian nationals spouse being unable to take up residence as the spouse of an European Union citizen.
Next, the Advocate General finds that the directive makes no reference to member state law in order to determine the nature of "spouse", even though that concept must be interpreted autonomously and uniformly throughout the EU.
While opinions issued by the European Court of Justice's Advocate General are non-binding, they're normally followed by the full court decision from the official justices.
"This is fantastic news and a landmark opinion for rainbow families", Sophie in 't Veld, the Dutch member of the European Parliament, told The Guardian. In its conclusions, known this Thursday, community lawyer opens door to a greater protection of rights of homosexual marriages in countries where it is not legalized.
Romania decriminalized homosexuality in 2001 but prohibits marriage between people of the same sex, and does not recognize same-sex marriages carried out overseas.
The country is moving towards holding a referendum on whether same-sex unions should be constitutionally banned and made illegal.
Last year, Kentucky clerk Kim Davis travelled to Romania with the Liberty Counsel, a right-wing Christian law group defined as an anti-LGBT hate group by the Southern Poverty Law Centre. Romania, which does not allow same-sex marriages, refused.