Senior Liberal Democrats have accused George Osborne of a "demonic" zeal to cut welfare, in comments that will further deepen the Coalition rift on the issue.
One said the Tories had a "19th century" determination to hammer the poor.
He also accused his party's Coalition colleagues of targeting those on benefits because they know they are "never going to vote [Conservative]".
Earlier this week Business Secretary Vince Cable made clear his party disagreed with Conservative plans for cuts after the 2015 General Election.
Mr Cable accused Mr Osborne of focussing on welfare cuts for "ideological" reasons.
The Chancellor surprised the LibDems earlier this month when he announced plans for an extra £25 billion of savings after the next election. Mr Osborne made clear that £12bn of them would come from welfare.
His announcement had been designed, in part, to put pressure on the Labour Party to set out what it would cut if it won the next election.
However, it kicked off a huge row both between the Conservatives and the LibDems.
One senior Liberal Democrat said: "The Tories have a demonic zeal to cut welfare. There is a 19th Century attitude to the poor.
"And it seems they have made the calculation, 'Look, these people are just never going to vote for us'."
In a speech on the UK economy, Mr Cable said: "It is a case which he [Osborne] is perfectly entitled to make in a party capacity, but let us all be quite clear that this is a political and ideological commitment."
He added: "The Liberal Democrats will reduce the debt burden but ensure this is not done at the expense of public services and the most vulnerable in society."
The Government has already cut billions of pounds of welfare spending since it came to power in 2010.
But ministers say they have not gone far enough to release people trapped by a lifetime on benefits.
Labour have, for the most part, attempted to stay out of the welfare row between the Tories and the LibDems.
At the weekend, however, Labour leader Ed Miliband said his party would "have to do more" to control welfare spending.
His comment followed Labour's promise to have the UK Government budget back in surplus by 2020. Mr Miliband said there would have to be major changes to "cut the costs of failure in the [welfare] system".
Labour has previously announced plans to strip some benefits from wealthier pensioners, including the winter fuel allowance, and indicated social security spending will have to be cut. But Mr Miliband warned "big reforms" were required.
He said: "If we are to tackle the deficit, we also have to do more to control social security spending. That means making tough choices this Government has ducked, such as scrapping the winter fuel allowance for the richest five per cent of pensioners.
"But to deal with welfare spending properly, we will need to make big reforms to cut the costs of failure in the system."