People claiming universal credit have been offered free use of Plaid Cymru phones to avoid helpline charges.
Party leader Leanne Wood said amid delays in payments, charging callers up to 55p a minute to check the status of their claim “adds insult to injury”.
The party said all Plaid MPs and assembly members would let claimants make the calls from their offices.
The Department for Work and Pensions (DWP) said people concerned about the cost could request a free call back.
Opposition parties and some Tory backbenchers have urged a pause in the nationwide rollout of universal credit – which replaces a range of benefits for working-age people – because of concerns over delays in claimants receiving their money.
Labour leader Jeremy Corbyn tackled Theresa May on the issue of the 0345 helpline at Prime Minister’s Questions on Wednesday, saying it was costing some of the nation’s poorest people 55p a minute to call on a mobile phone.
In a joint statement on Thursday, Plaid MPs Hywel Williams and Liz Saville Roberts said their constituency offices in the Gwynedd towns of Caernarfon and Dolgellau respectively would be available for claimants to make such calls on the party’s phones.
“It is shocking that those trying to claim universal credit face being charged for the privilege of simply speaking to someone about their claim,” the MPs for Arfon and Dwyfor Meirionnydd said.
“Notwithstanding the barriers already faced by many claimants, such as spiralling debts, homelessness and evictions, charging people who are broke to find out the status of their claim is absurd.
“I hope they will drop this outrageous charge as soon as possible.”
On Friday, Plaid leader Leanne Wood said all the party’s MPs and assembly members would allow claimants to call the helpline from their constituency offices.
“The roll-out of the universal credit has caused untold misery for the thousands of people who have already faced receiving their payments late or not at all,” she said.
“The revelation that the Tory UK Government is charging people 55p a minute just to call the universal credit helpline adds insult to injury.
“People who are already suffering as a result of the Tories’ botched reforms shouldn’t have to face a further hit in the form of extortionate phone bills which they may not be able to afford.”
Meanwhile Conservative AM Mark Isherwood has written to Work and Pensions Secretary David Gauke urging him to reconsider the helpline charges.
He claimed the situation was made worse by the fact that while some people were charged for calling the English-language helpline, calls to the Welsh-language helpline on an 0800 number were free.
A DWP spokeswoman said: “Applications for universal credit are made online and claimants then arrange their first appointment with their work coach over the phone.
“This call is charged at local rates which are set by providers and are free for many people as part of their call package.
“If someone is concerned about the cost, they can request a free call back.”