Solo parents on the domestic purposes benefit will have to work or undertake training when their children reach school age if National wins power.
Party leader John Key today unveiled National's policy on social welfare benefits.
He said National would not introduce a work-for-the-dole or a community wage scheme.
"Instead we will be going one better and will focus on long-term unemployed by requiring them to get paid work and get off the benefit," he said.
The announcement was part of a raft of policies aimed at Mr Key's goal of getting beneficiaries into work to address what he has described as an "emerging underclass".
He has criticised Labour for its DPB policy, saying in 2002 that it had led to the situation "where people have been, for want of a better term, breeding for a business" - a statement Labour has since used against him.
Today, Mr Key announced that National would make many on the DPB spend at least 15 hours a week in part-time work, training or actively job-seeking - similar to obligations faced by those on the unemployment benefit.
"Paid work is the route to independence and well-being for most people and is the best way to reduce child poverty," he said.
At present, domestic purposes beneficiaries have to prepare a future employment "goal", but there are no work or training obligations.
Mr Key was expected to say many of those on the DPB whose children are at school "can and should" work to help to reduce family poverty, and argue that making work or training an obligation of getting a benefit is effective at reducing benefit numbers.
The policy will apply to those whose youngest child is aged 6 or over and will affect more than 38,400 single parents - about 40 per cent of the 96,000 on the DPB.
Prime Minister Helen Clark said National's policy was too tough on single parents.
"I see they've got the hoary old beat up on single parents," she told TV One's Breakfast programme.
"I've got one view on that - whatever we do with single parents we have got to be guided by what is in the best interest of the children and it's not always in the best interest of every child that mum is at work all day.
"It has to be worked through with individual families."
Helen Clark said the Government's Working for Families programme was a success and the number of people on the Domestic Purposes Benefit (DPB) was dropping.
"And the truth is most people on the DPB are not there for very long," she said.
"I'm all in favour of supporting single parents to get into work, but in the final analysis we have to be guided by what is in the best interest of the children in a particular family."
Helen Clark said circumstances differed, with some solo parents looking after children with cystic fibrosis or autism.
"They've got a lot of things going on in their lives and to tell a single parent they have a work obligation can be too tough," she said.
Under its welfare policy, National will also provide a carrot to encourage people on benefits to take on more part-time work. It will allow beneficiaries to earn up to $100 a week before their benefits begin to drop - up from the current $80.
The total getting the DPB has dropped from 108,690 in 2003 to 96,400 in June this year - a result Labour has attributed to policies such as Working For Families.
However, the proportion of those on the DPB who have declared income from part-time work has shrunk over the past five years from 23 per cent to 19 per cent.
More than 10 per cent of DPB recipients have been on the benefit for 10 years or more and a quarter have been on it for four to 10 years.
Mr Key is also expected to announce the party's position on the single core benefit which Labour is working towards introducing. Under the scheme, benefit names such as "DPB" and "Invalids" will be scrapped.
Instead, beneficiaries will be given a personal tailor-made scheme depending on their ability to work, or their training needs.
Although New Zealand has recently had record low unemployment rates, National's welfare spokeswoman, Judith Collins, has been scathing of Labour's handling of social welfare policy, arguing it has moved beneficiaries on to sickness and invalids benefits to hide the true level of unemployment.
More than 38,400 single parents of children aged 6 or over are on the DPB.
More than 10 per cent of recipients have been on the benefit for 10 years or more.
25 per cent have been on it for between four and 10 years.
Unlike those on the unemployment benefit, there is no requirement for single parents on the DPB to work or train while they have dependent children.