Parents could be subjected to random checks on their work hours if they claim a proposed new childcare subsidy.
The federal government's childcare package unveiled in parliament on Wednesday includes a new work-or-learn activity test for parents claiming childcare hours.
How much they get back through a new means-tested subsidy will vary based on hours spent working, studying or volunteering in a fortnight.
A parent who spends eight hours working or learning will get 36 hours of subsidised child care a fortnight; those who do more than 48 hours will get 100 hours.
Education Minister Simon Birmingham believes it is an "incredibly fair" proposition.
"Those families working the hardest receive the greatest benefit," he told reporters in Canberra.
The only way parents will lose out is if they fail to meet the activity test, he conceded.
"And the activity test is ... incredibly light-touch," the minister added.
Parents are also being warned to expect random sample spot checks of their activity.
The Department of Education is developing the test for the childcare package's expected start date of July 2017, pending parliamentary approval.
"The approach will draw heavily on the Department of Human Service's current, well-established payment integrity processes," the department said in a statement to AAP.
But the government needs $3.2 billion for the new package, and it wants to use changes to family tax benefit payments to pay for it.
On Wednesday it reintroduced legislation previously stymied by the Senate that includes $4 billion in cuts to annual family bonuses.
The measures mean families will no longer receive family tax benefit supplement Part A of about $726 and Part B of $354.
Social Services Minister Christian Porter labelled the two pieces of legislation "twins", saying the childcare package was dependent on family payment cuts.
With Labor opposed to the abolition of supplements, the minister is working to convince Senate crossbenchers for their support.
"We'll do whatever we can in those discussions to convince the cross bench," he said.
The opposition said the family payment cuts were a cruel Christmas present to families and criticised the "embarrassing" lack of detail in the childcare bill.
Labor early childhood spokeswoman Kate Ellis said while it was unclear how many families would lose out, she expected hundreds of thousands would be worse off.
Meanwhile, the Senate called on the government to table all documents relating to the childcare package, including economic modelling on the impact of the reforms on families.
