Labour was accused of trying to “scare” older voters with claims it is storing up a £35 billion pension blackhole after the election.
Party election strategist Jonathan Ashworth claimed Tory plans to abolish national insurance would mean the end of the state pension.
He said severing the link between contributions and pension entitlement created uncertainty about future claims.
But Chancellor Jeremy Hunt hit back at Labour’s “pension bombshell dossier”.
He said: “This is just scaremongering. The value of NICs receipts do not determine the NHS budget or the value of pensions. Those decisions are taken entirely separately.”
Mr Hunt has cut 4p in the pound off national insurance contributions since November and used his budget to set out plans to scrap the work tax altogether in the future.
The Chancellor said his ambition to abolish contributions will not happen in one election cycle.
Appearing before the Treasury Committee on Wednesday, the Chancellor said: “It won’t happen in one Parliament, but it’s a long-term ambition.
“If we do that, that will be the biggest tax simplification of our lifetimes.”
Labour claimed the average pensioner faces an £800 tax hike that would wipe out the gains made through the triple lock if NICs were merged with income tax.
It said the plans would cost £46 billion overall which would hit pension and health spending or lead to higher taxes.
Labour Party analysis found 80% of NICs receipts are earmarked for the National Insurance Fund, which mainly covers pension payments, and the rest goes to the NHS.
It claimed abolishing NICs would put around £35bn of funding for the state pension at risk.
Mr Ashworth, shadow paymaster general, said: “The future of the state pension is on the ballot paper at the next general election.
“The Tories’ £46 billion unfunded tax plan to abolish national insurance can only lead to higher borrowing, higher taxes on pensioners or the end of the state pension as we know it.
“Ministers need to come clean with the British people and start answering these basic questions.”
A Tory source said: “They shouldn’t be scaring elderly pensioners like this.”
