Independent ACT senator David Pocock has called on the federal government to bring forward changes to the sole parent payment amid concerns families will be left $100 a week worse off under current transition arrangements.
Budget legislation to be debated this week includes a move to expand access to Parenting Payment Single to include families whose youngest child is less than 14 years, up from the current threshold of eight years.
But the change will not be implemented until September 20, and Senator Pocock said in the interim around 5000 single parent families, including about 70 in the ACT, will be forced on to the much lower JobSeeker payment because their youngest will turn eight years old, costing them $204.20 a fortnight.

The senator has urged the government to speed up the welfare shift.
"Forcing some 5000 single parents to lose over $200 a fortnight in support, even just for a few months while waiting for changes announced in the budget to come into effect, is very disappointing given the cost-of-living challenges they are facing," the senator told The Canberra Times.
The government said about 57,000 people nationally will benefit from the change to increase maximum basic rate from $745.20 to $922.10 a fortnight.
READ MORE:
The change goes a significant way to reversing the 2006 Howard government decision to slash the youngest child age eligibility threshold from 16 years to eight.
Implementation of this shift was grandfathered, but in 2012 the Gillard government decided to end the arrangement, forcing thousands of single parents, the vast majority women, on to lower unemployment benefits once their youngest turned eight.
Parenting and welfare groups have been lobbying for the reinstatement of the 16 years threshold, but the change unveiled in the budget has been broadly welcomed as an important step towards that goal.
But Senator Pocock demanded the government go further and implement the change as soon as possible.
"The pandemic proved that the government can make changes quickly when needed," he said.
"I welcome the government reversing changes that a decade ago penalised single parents, but encourage them to do better in implementing this change."
But Social Security Minister Amanda Rishworth defended the time that will be taken to introduce the expanded eligibility criteria for the payment.
"We need to factor in changes to the back end of Services Australia to accommodate our budget measures and ensure the systems that deliver them have the time required to prepare and adjust," Ms Rishworth said.
The minister added that September 20 was also the date income support payments, including the Parenting Payment Single, would be indexed and the updated amount was yet to be determined.
"Our budget measures have been carefully calibrated to ensure those Australians who rely on the income support safety net get some extra relief with cost-of-living pressures," she said.