The House of Lords vote to block tax credit cuts creates a "big constitutional issue", leader of House of Commons Chris Grayling has said.
The former Conservative Justice Secretary said it "cannot be right" for the unelected Lords to stand in the way of the changes.
Mr Grayling told Good Morning Britain: "Of course it's a difficult decision to have to take but we have a big task still ahead of us to balance the nation's books and create a sound financial foundation for the next generation.
"What shouldn't happen is unelected peers breaking the traditions of decades and throwing out a financial measure in the wake of three votes in the House of Commons which said we need to go ahead with this."
Mr Grayling said the tax credit cuts were part of a package of changes, including free childcare and cuts to social rents, designed to help working families.
They are not there to interfere with the settled will of the House of Commons, warned Boris Johnson.
A working mum who would be hit by Tax Credit cuts spoke to ITV News ahead of the House of Lords vote on the changes.
Peers will have to decide whether to delay changes to the tax credits bill, review them or scrap it altogether.