David Cameron has come under fire after calling for fathers who abandon their families to be "stigmatised" by society in the same way as drink-drivers.
The Prime Minister signalled a new onslaught on "runaway dads", saying they should be made to feel the "full force of shame" for their actions.
However campaigners warned that efforts to hold fathers responsible for their families are being undermined by Government plans to charge mothers who use the Child Support Agency to collect money they are owed.
"David Cameron is right that single mums - and indeed single dads - do a heroic job," said Fiona Weir, the chief executive of the single parents' charity Gingerbread.
"But those same parents are about to have Government support ripped away from them if they need help securing child maintenance payments from their child's other parent."
Shadow home secretary Yvette Cooper accused Mr Cameron of offering "hollow words" at a time when the Government is withdrawing support for families.
"David Cameron's claim to support families and crack down on runaway dads is utterly disingenuous," she said. "His Government is making it much easier for deadbeat dads to run from their responsibilities by charging mums to use the Child Support Agency.
"And now he wants to reward runaway dads who remarry with a marriage tax break, whilst still cutting tax credits for the mums left behind holding the baby."
Writing in The Sunday Telegraph in an article to mark Father's Day, Mr Cameron said it "simply isn't acceptable" for single mothers to be left to bring up their children on their own.
"It's high time runaway dads were stigmatised, and the full force of shame was heaped upon them," he said. "They should be looked at like drink-drivers, people who are beyond the pale. They need the message rammed home to them, from every part of our culture, that what they're doing is wrong - that leaving single mothers, who do a heroic job against all odds, to fend for themselves simply isn't acceptable."