The gaps in the federal government's paid parental laws were highlighted in the case of a Tasmanian family, who were asked by the Tasmanian Government to adopt a baby boy at short notice.

The family were then denied the leave entitlements because they hadn't worked 330 hours prior to the adoption.

The decision appears to set adopting parents apart from natural parents, who are exempt from meeting the government's work test if their birth occurs unexpectedly.

The Tasmanian adoption came after the birth mother asked for her new baby boy to be kept with his older brother, who the family had adopted some time earlier.

The mother agreed, but had only recently returned to work and had not completed enough hours to satisfy the federal government's criteria.

The family was denied paid parental leave entitlements last year, a decision they fought in the Administrative Appeals Tribunal.

The tribunal this week confirmed the family was not eligible, but described the decision as an "unfortunate outcome", the circumstances of which were probably not contemplated by lawmakers.

Birth parents are allowed an exception to the 330 hour work test in cases where there is a premature birth or complication with pregnancy, yet families who adopt in unforeseen circumstances are not.

The family's lawyer argued to the tribunal that the paid parental leave legislation intended to provide the same rights to adopted parents.

He said that, under the United Nations Convention on the Rights of the Child, the government was required to act in the best interests of the child.

The child's interests, the lawyer argued, were best served by affording adopting parents the same rights as birth parents.

But the tribunal found there was no specific provision about unforeseen adoptions and exemption from the 330 hour work test in the 2010 paid parental laws.

"Whilst the tribunal is sympathetic, there simply is no provision in the Paid Parental Leave Act 2010 that accommodates [the mother's] particular circumstances such as to qualify her for the work test and thus eligible for paid parental leave for her son," the tribunal found.

"It is indeed an unfortunate outcome and one presumably not contemplated by the legislature."

The decision means the family will miss out on the entitlements despite meeting all other eligibility requirements except the work test.

The family did receive paid parental leave for their earlier adoption of the baby's older brother.