Benefit freezes will deprive two million claimants of £2billion, Labour say.
Disabled people are £660 down and that could hit £1,000 by April after they lose out on a £20-a-week rise given to other Universal Credit claimants.
The increase, due to Covid, was not given to Employment and Support Allowance claimants.
Employment Secretary Therese Coffey said necessary computer system changes would take months and a future increase could not be ruled out.
But Shadow Pensions Secretary Marsha de Cordova said: “It is time the Government ended this discrimination.”
The Tories won’t say whether the £20 rise will extend beyond April or whether disabled people on ESA will ever get it.
Lucy Hamilton, of poverty action group the Joseph Rowntree Foundation, said: “Millions face fear over Christmas and even greater hardship next year.
"It’s important that it’s rectified now.”
It comes the day after it was reported tens of thousands of people will see their Universal Credit payments cut this Christmas.
That's because a measure put in place to try and protect people who've recently started using the six-in-one benefit is set to run out.
And the end of the so-called 'grace period' could hit 160,000 households could be affected, Wales Online reports.
The grace period exempts people from the benefit cap - which limits the total amount of money working age people can claim regardless of what they qualify for on other measures.
It applies if you get Housing Benefit or Universal Credit, and your benefits will be capped if you get more than the limit that applies for your circumstances.
And the number of people affected by the cap has more than doubled since coronavirus hit Britain.