The Supreme Court is considering the legality of Government financial measures that are hitting British citizens who want to bring spouses into the country.
The Immigration Rules were amended in 2012 to include a mandatory requirement that a UK sponsor must have a minimum gross annual income of £18,600 before they can invite in partners from non-EEA (European Economic Area) states.
Previous rules only required a couple to demonstrate they could maintain themselves without recourse to public funds.
A High Court judge ruled the introduction of the "minimum income requirement (MIR)", which increases if there are children, was an unjustified interference with human rights.
But the Court of Appeal allowed an appeal by Home Secretary Theresa May.
Now the Supreme Court, the highest court in the land, is to make a final ruling in a number of linked cases.
The Divided Families Campaign says the Home Secretary's policy is "obstructing family reunion for tens of thousands of people".
The case centres on judicial review applications brought by two British citizens, referred to as AM and SJ who cannot meet the requirement and MM, a refugee from the Lebanon in a similar position, and his nephew AF.
In another case, SS, from the Democratic Republic of the Congo, is challenging a refusal of entry clearance as the spouse of a refugee who became a naturalised British citizen, but whose earnings are below £18,600.
Immigration tribunals allowed her appeal under Article 8 (right to private and family life) of the European Convention on Human Rights. But the appeal court ruled she had not demonstrated "compelling circumstances" justifying the granting of entry clearance.
High Court judge Mr Justice Blake ruled in the judicial review challenges that the financial requirements set out in rules introduced in July 2012 amounted to a ''disproportionate interference with a genuine spousal relationship''.
Three appeal judges - Lord Justice Maurice Kay, Lord Justice Aikens and Lord Justice Treacy - disagreed and said the requirements ''are lawful''.
Lord Justice Aikens said in the lead judgment that he was "very conscious of the evidence submitted by the claimants to demonstrate how the new MIR will have an impact on particular groups and, in particular, the evidence that only 301 occupations out of 422 listed in the 2011 UK Earnings data had average annual earnings over £18,600".
But the Home Secretary had analysed the effect of the immigration of non-EEA partners and dependant children on the benefits system and "the link between better income and greater chances of integration", said the judge.
She had "struck a fair balance between the interests of the groups concerned and the community in general.''