The charity Age Scotland has told the Scottish Parliament’s social security committee the new rules could have a “devastating impact” on many older people.
Mixed age couples affected are those where one is below pension age and the other receives a low state pension.
Pension Credit tops up the state pension to £163 a week for a single person and £248.80 for a couple.
But the Universal Credit rate, which would apply to new mixed age couple applicants, is just £115 a week - a difference of around £7,000 a year for those on the lowest incomes.
You may also be interested in:
Age Scotland said: “The move was quietly announced through a Written Ministerial statement on a busy Brexit vote day in the UK Parliament in January. The new changes will go in effect on May 15.
Until now, mixed age couples have been able to choose whether to claim Pension Credit or working age benefits, but from May 15 a couple will have to wait until they both reach their State Pension Age in order to claim Pension Credit.
Age Scotland says those who are not able to recveive Pension Credit will also lose out on cold weather payments, housing benefit, Council Tax Reduction and social fund funeral payments - and may not even be entitled to the warm home discount.
Age Scotland’s Chief Executive, Brian Sloan, said: “This outrageous new policy will have a devasting impact to Scotland’s poorest pensioners and will make older couples of mixed age poorer for living together.
“When the move was announced the UK Government did not know how many people it would impact.
“Weeks later it emerged that it would impact 15,000 people in 2019/20, 30,000 the following year and 40,000 the year after that - but still no official assessment for Scotland.
“We estimate that at least 1,500 of the poorest pensioners in Scotland will be hit next year, and double that the following year. It’s not acceptable.
“We urge the UK Government to reverse this move through the primary legislation it requires as it will leave thousands of our poorest pensioners worse off.
“While challenging, the Scottish Government should also look at how it could mitigate against the effects of this disastrous policy”.
Meanwhile he says it is vital that older people who could be entitled to pension credit, but are not already claiming it, receive their due entitleme
They are urged to call Age Scotland’s free and confidential phone helpline on 0800 12 44 222.