Same-sex couples denied the opportunity to marry in Northern Ireland are being subjected to unlawful discrimination, the Court of Appeal heard yesterday.
Senior judges were told a failure to introduce rights available to those living in the rest of the UK cannot be justified.
The claims were made as two gay couples renewed their legal challenge to the ban on them getting wed.
Grainne Close and her partner Shannon Sickles, along with Chris and Henry Flanagan-Kane, are seeking to overturn a ruling that the prohibition does not breach their human rights under European law.
In 2005 they became the first couples in the UK to enter civil partnerships, cementing their relationships in ceremonies at Belfast City Hall.
But unlike England, Scotland, Wales and the Republic of Ireland, Northern Ireland has still not legalised same-sex marriage.
Last year a judge dismissed the case after finding that it was a matter for the Stormont administration rather than the courts.
Ronan Lavery QC argued that the failure by the state to include the people of Northern Ireland in same-sex marriage legislation breached their human rights.
Prior to the collapse of devolution MLAs held a number of votes on the issue - with a narrow majority in favour of the move back in November 2015. However, the DUP deployed a petition of concern mechanism to block the motion.
The court heard that 15 out of close to 50 jurisdictions within the Council of Europe have now brought in same-sex marriage. But Strasbourg has left it up to individual states to decide on the policy.
Pressed to define the obligation allegedly being breached, Mr Lavery submitted that once the marriage rights were brought in they should apply equally to all parts of the UK.
The challenge is being resisted by lawyers for the Department and the Attorney General, John Larkin QC.
Mr Larkin argued that the applicants lacked legal standing to bring the action.
Tony McGleenan QC, for the Department, accepted differential treatment between heterosexual and same-sex couples but he said the legitimate aim was about preserving traditional marriage.
Provisions are made for same-sex couples through the availability of civil partnerships, the barrister argued.
Mr McGleenan is to make further submissions when the case resumes on Thursday.
Ms Sickles said outside court: “It’s exhausting to feel discriminated against, its frustrating, it’s enraging and its unfair.”