A woman denied payments from her late long-term partner's occupational pension will find out the result of a Supreme Court battle on Wednesday.
At a hearing last year, justices at the UK's highest court heard argument on her behalf that she was the victim of "serious discrimination".
Denise Brewster, from Coleraine, Northern Ireland, has challenged a ruling that she is not automatically entitled to a "survivor's pension" as she would have been if the couple had been married.
Five justices heard Ms Brewster and Lenny McMullan lived together for 10 years and owned their own home.
They got engaged on Christmas Eve 2009 but Mr McMullan died suddenly between Christmas night and the early hours of Boxing Day morning.
Mr McMullan had worked for 15 years for Translink, which runs Northern Ireland's public transport services. He was paying into Northern Ireland's local government pension scheme.
The scheme is governed by rules made under the Local Government Pension Scheme (Benefits, Membership and Contributions) Regulations (Northern Ireland) 2009.
Under the regulations, married partners automatically obtain a survivor's pension but unmarried partners only receive a pension if there has been compliance with an "opt-in" requirement.
This involves the pension scheme member nominating their partner for payments by giving the Northern Ireland Local Government Officers' Superannuation Committee (Nilgosc) a declaration signed by both partners.
Although she met all the other criteria, Nilgosc refused Ms Brewster a survivor's pension because the committee had not received the appropriate nomination form from Mr McMullan.
The High Court in Northern Ireland allowed her legal challenge against the refusal but the Court of Appeal overturned that decision and the Supreme Court has been asked to make a decisive ruling.
Helen Mountfield QC, representing Ms Brewster, now in her early 40s, asked the court to declare that the opt-in nomination rule in the 2009 regulations breaches Article 14 and Article 1 of the First Protocol of the European Convention on Human Rights. Nilgosc contested the action.
Article 14 prohibits discrimination in the way human rights laws are applied and the First Protocol protects a person's right to property and the peaceful enjoyment of possessions.
Ms Mountfield told the justices - deputy president Lady Hale, Lord Kerr, Lord Wilson, Lord Reed and Lord Dyson - the nomination rule was having "a seriously discriminatory effect".
Cohabiting partners were being discriminated against compared with spouses automatically entitled to the pension.
While raising funds to take her case to the Supreme Court, Ms Brewster said: "My case is simple: bureaucratic rules like this which discriminate against long-term cohabitees should not be permitted."
She added: "A positive decision from the Supreme Court is likely to impact on discrimination against cohabitees across a wide range of areas, not just pension rights."
Lawyers for Nilgosc and the Department for Communities for Northern Ireland argued the regulations were reasonable and served a legitimate aim.
They asked the Supreme Court to uphold the appeal court's majority ruling that requiring a cohabiting partner to be "nominated" was justified and proportionate.