Over 9,000 families are to lose their One-Parent Family Payment from today, when a previously announced measure comes into effect.
Changes to the eligibility criteria for the payment were announced two years ago, gradually reducing the number of those receiving the benefit.
The change is dependent on the age of the claimant's children, along with when the payment began.
Those who have relied on the payment will be offered a range of supports by the department.
By this time next year, almost 60,000 families will have lost the One-Parent Family Payment.
The Chief Executive of One Family, an organisation that lobbies for equality for one-parent families, has said the Government has not sufficiently invested in the supports that are necessary for one-parent families that will lose their payment today.
Speaking on RTÉ's Morning Ireland, Karen Kiernan said the removal of this payment from some families, to try to encourage lone parents into the workplace, has not been planned for.
Ms Kiernan said services are required to ensure parents have the appropriate skills to re-enter the workforce as well as childcare facilities to allow them to return to work.
One Family acknowledges that the scheme needs to be reformed to become an active encouragement back to work for lone-parents, but Ms Kiernan said if the appropriate services are not in place, families will find it difficult to make ends meet, and may have to give up part-time work.
She added that the removal of the payment today is counter-intuitive to what the Government is trying to achieve, and insufficient planning will leave families who are already struggling worse off.
"What it actually means for the nearly 60,000 families that are going to be moved off next year is that a lot of them are going to be down money, and they are already extraordinarily poor families, who are finding it difficult to make ends meet", she said.