Shadow chancellor John McDonnell has said Philip Hammond must stop "giving money away" to the banking sector and instead invest more in Britain's beleagured public services.
Jeremy Corbyn's right-hand made the comments on Twitter as MPs continue to demand that Hammond end a cut to the bank levy which was introduced in 2015.
Labour says the tax break has given £4.7 billion to the financial sector, according to The Mirror.
Although a motion to cancel the cut and give the extra money to children's services has already been vetoed, McDonnell believes Hammond still has time to make a u-turn.
He wrote: "Hammond still has a chance to change his mind and stop this tax giveaway to the banks.
"Our public services are in crisis. Now is not the time to be giving money away."
Despite the defeat of the earlier motion, MPs are now to debate measures which would increase the scrutiny on Britain's banks.
The measures include a register which will show how much each bank contributes towards the levy, as well as a review of the effectiveness of the tax.
Labour's treasury spokesman Peter Dowd said: “We are simply asking for greater transparency over this unfair giveaway to already profitable big banks at a time when our public services and working families are struggling just before Christmas.
“These planned cuts in the rate of the Bank Levy will see billions handed out to the major banks by 2020, which now opens up questions over the effectiveness of this tax as a revenue raiser.
“Philip Hammond still has the choice this week to change direction.
“He can either choose to end this injustice in the Finance Bill, or choose for Christmas to come early for the bankers and act like Scrooge to the rest of us.”