A small religious group with a pre-existing objection to vaccination is the only group exempted from the new "no jab no pay" rule in Australia.
And the government is keen to keep it that way.
Social Services Minister Scott Morrison won't name that group, lest it promote a sudden rush in membership.
"There is only one, it is a very small religion and I am not about to encourage people to line up with it just to get another crack at an exemption," he said on the Nine Network.
Under the plan announced on Sunday, parents who decide against immunisations could be up to $15,000 worse off per child.
They would lose a childcare benefit of up to $205 a week, the childcare rebate of up to $7500 a year or the Family Tax Benefit A annual supplement of up to $726.
Children can still be exempted on medical or religious grounds, but Mr Morrison warns the latter exemption is "very narrow".
That contrasts with the US where the constitutional guarantee of freedom of religion has allowed creation of religions whose tenets specifically exempt members from state requirements for vaccination of their children. Membership is available to anyone for a small fee.
Mr Morrison said no mainstream religions had registered vaccination objections with the Australian government.
But the number of conscientious objections has continued to grow, more than doubling in the last decade.
The government estimates about 39,000 children under seven have not received immunisation because their parents are vaccine objectors.
Now it's seeking to close off most vaccination exemptions based on religious grounds.
A spokesman for Mr Morrison said this religious particular group had a pre-existing official exemption based on their religious beliefs.
"We have also said we will keep a close eye on that measure as well in case it's abused. We will look to take action on that if necessary," he said.