The Church of Scotland, the Baptist Union, the Methodist Church and the United Reformed Church called the cap "indefensible" before it came into force today and are urging the government to make a U-turn.
The cap means that families can only receive a maximum £20,000 in certain benefits per year - or £23,000 if they're in London.
Previously the cap was £26,000.
The cap is part of £12bn of savings from the welfare budget announced by the previous Chancellor George Osborne.
It's been reported total welfare spending is expected to come to about £231 billion in 2015/16 - more than a third of all public spending.
The cap will affect approximately 64,000 families and government figures suggest 95 per cent of them have children.
It will not apply to families where one member works at least 16 hours a week, and excludes Disability Living Allowance and Personal Independence Payment, among others.
Speaking on Premier's News Hour Rev Dr Richard Frazer, convener of the Church of Scotland's Church and Society Council, said: "The reality of the situation is that there is absolutely no evidence that you can change people's behaviour by reducing their income.
"All you do is drive people further into the spiral of debt and of lack of hope and ways in which people's lives begin to unravel.
"There are churches that are doing sterling work to support vulnerable people and begin to get themselves into a situation where they can look for and take on work. That's the kind of work that the churches do so well and that the government needs to invest in and support."
A Department for Work and Pensions spokesman said: "We are committed to helping lone parents into a job which fits in around their caring responsibilities, which is why we are doubling the amount of free childcare available.
"We know that work is the best route out of poverty, and there are now record numbers of lone parents in work.
"The benefit cap provides a clear incentive to move into a job, even if it is part time, as anyone eligible for working tax credits is exempt."
Listen to Premier's Aaron James speaking to Rev Dr Richard Frazer on the News Hour:
