Thousands of families will be placed under "unfair pressure" due to welfare system reforms that are coming into force, a charity has warned.
Gingerbread urged the Government to delay plans to tell single parents not in paid work, whose youngest child is five or six-years-old, that they will be required to find a job or face potential cuts to their benefits.
The group, which campaigns on behalf of single parents, said that at a time of rising unemployment, the move could "cast adrift" 100,000 people.
Chief executive Fiona Weir said: "The proposed timing of this change is disastrous and will plunge thousands of single parents into a stagnant job market with little prospect of finding work that fits around their caring responsibilities.
"In previous years, single parents have been given plenty of notice of these changes and time to prepare, but the Government is rushing this legislation through and will catch single parents unawares.
"It makes much more sense to delay the change until 2013 when newly-announced childcare support will be available for part-time jobs, which will help single parents of young children balance work and parenting."
Gingerbread said single parents will start receiving letters from Friday telling them of changes in the conditions for receiving income support.
The charity said it was the first step to their income support ending early next year, at which point they will have to claim Jobseeker's Allowance, or another benefit, instead.
A Department for Work and Pensions spokesman said: "We know that many lone parents want the opportunity to get back into work earlier and that work is the best route out of poverty. This is why we are bringing forward and increasing the support we offer to lone parents.
"Getting a good balance between work and family responsibilities is important for every parent, which is why we will actively support lone parents so that they can get that balance right to take account of caring responsibilities and childcare."