Work and Pensions Secretary Liz Kendall has said welfare changes are "never easy and rarely popular, perhaps especially for Labour governments" but that she would not "resile" from difficult decisions.
Speaking in central London, she insisted that, without change, there was a "risk" the welfare state "won't be there for people who really need it in future".
Government measures, which include stricter tests for claiming some benefits and reducing payments for others, have caused unease among some Labour MPs.
Poole MP Neil Duncan-Jordan told the BBC he was "extremely concerned" that the government was going "further and faster and doubling down" and urged ministers to "pause" the cuts.
He added that there was "a very healthy debate inside the Labour Party at the moment about how we should be raising funds rather than cutting benefits".
It comes as a memo – seen by the Daily Telegraph – appears to show that earlier this year Deputy Prime Minister Angela Rayner's department urged the Treasury to consider new tax-raising measures.
Chancellor Rachel Reeves has said she would not borrow to fund day-to-day spending.
