Labour has accused the UK Government of “disgracefully” allowing the estimated £332 million in pension credit to go unclaimed.
The charity Independent Age believes there are 123,000 households in Scotland with pensioners eligible for pension credit that have not claimed it.
It is calling for more to be done to help the poorest pensioners access the money.
Shadow Secretary of State for Scotland Lesley Laird backed the charity’s call.
She said: “The last Labour Government cut pensioner poverty but the Tories have disgracefully allowed it to go up on their watch.
“It is shocking that Scotland’s poorest pensioners are missing out on more than £300 million in vital support.
“The Tories’ idea for encouraging people to apply for pension credit - an ‘online toolkit’ - would be laughable if this wasn’t so serious.
“Across the UK, the poorest pensioners have missed out on £7 billion of Pension Credit since the last election, which means vulnerable people are being left without much-needed income.
“The Tories must right this wrong immediately and do more to increase take-up of Pension Credit.”
A spokesman for the Department for Work and Pensions said: “Pensioner poverty rates have fallen dramatically in recent years with relative pensioner poverty rates halved since 1990.
“We want to maintain this achievement and we want everyone to claim what they are entitled to.
“Everyone who claims their state pension receives a letter which encourages them to contact us directly over the phone to discuss their pension credit entitlement.”