Heidi Allen, the MP for South Cambridgeshire, used her maiden speech in the Commons on Tuesday to deliver a withering critique of George Osborne's plans to cut tax credits.
The Conservative MP, elected in May, said she could not stay silent on the issue any longer as she urged the Chancellor to reconsider.
Ms Allen warned that the "poorest and most vulnerable" would be hit by the £4.4bn package of cuts, leaving them with the choice of eating or heating to make ends meet and said it was a betrayal of her party's traditional support for working families.
She told MPs:
The Prime Minister has asked us that everything we do must pass the family test. Cutting tax credits before wages rise does not achieve that. Showing children that their parents would be better off not working at all does not achieve that.
Sending a message to the poorest and most vulnerable in our society that we do not care does not achieve that either.
I believe the pace of these reforms is too hard and too fast. As these proposals stand, too many people will be adversely affected. Something must give.
While explaining that she backed the principle that tax credits should not be used to subsidise low pay, she said she believed the timing of the cut was wrong.
For those of us proud enough to call ourselves compassionate Conservatives, it must not be the backs of the working families we purport to serve.
It isn't sustainable and it sends the wrong message about the kind of country and the kind of people that we want to be.
A succession of backbenchers called in the Commons last night for a rethink of the plans following claims that 3.2m people will see their tax credits cut.
Mr Osborne insists he is not considering watering down the scheme, but increasing numbers of senior Conservatives believe he will be forced to offer some concessions next month in his spending review.