The Government is being urged to reverse planned changes to the one-parent family support grant.
Fianna Fáil said it was ironic the Minister for Social Protection Joan Burton was trying to incentivise people back to work by "rewarding them with less".
As of July 2, single parents who are working and have a child over the age of seven will see a reduction in the amount of hours they are allowed to work before receiving the payment.
Limerick TD Willie O'Dea says it was an unfair hit on some of the most vulnerable families.
"All we can do is to urge the Government not to proceed with this change," he said.
"At the moment, a lone parent with kids can get the lone parent's allowance until the youngest child reaches 14.
"Bringing it down to seven will hurt a lot of very vulnerable people. It's going to hurt those lone parents who are going out to work, which is hugely ironic."
Carers have been expempted from the cuts.
Changes to eligibility criteria were flagged by the Coalition more than two years ago but will come into effect in July.
Under the planned changes in July, more than 30,000 parents will lose their one parent family payments. They will be moved onto jobseekers’ payments if their child is seven.
Ms Burton said the changes were to get lone parents out of the poverty trap and into work. Instead of getting payments, families will be offered education and training supports.
Some parents’ groups claim adults could be up to €80 a week worse off under changes.
Ms Burton said there would be no financial change for some lone parents. While all exiting the scheme will be moved onto jobseeker’s allowance, her department said payments would remain the same where people are earning under €60 per week.
This means parents taking up part-time work or not working will get the same payments. Those who earn over €60 a week though, will face reductions in payments.