Same-sex couples that have been denied the opportunity to marry in Northern Ireland are being subjected to unlawful discrimination, the Court of Appeal has heard.
The argument was put forward by legal teams representing Grainne Close and her partner Shannon Sickles, along with Chris and Henry Flanagan-Kane.
The two couples are seeking to overturn a ruling that the prohibition does not breach their human rights under European law.
They were the first couples in the UK to enter civil partnerships, having cemented their relationships in ceremonies at Belfast City Hall in 2005.
Unlike England, Scotland and Wales - as well as the Republic of Ireland - Northern Ireland has yet to legalise 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.
"It's unlawful discrimination against the applicants on the basis of their sexuality," he contended.
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.
He rejected "this notion that gays and lesbians should be happy enough with civil partnerships".
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.
"What we are dealing with is not an act of the Assembly," he told the three judges.
As the appeal continued, the two couples told of their continued dismay at the bar on getting married.
Speaking outside court, Ms Sickles said: "It's exhausting to feel discriminated against, its frustrating, it's enraging and its unfair."
Her partner, Ms Close, added that they were left relying on the courts to "step up to the mark" in the absence of Stormont.
"We don't want to be here, but it's our only avenue," she said.