Javed Tahiri was told his application failed because his mother did not have permission from his father to bring the children to Australia, despite the fact that his father has been missing, feared dead, for a decade.

In his father's absence, the department required evidence that his father's family approved of the move, but this had proved difficult because his mother and siblings had fled to Pakistan and were living in fear in Quetta, says Joel Townsend, from Victoria Legal Aid.

Mr Townsend is hopeful of winning a High Court challenge to the decision, which was heard on Friday, and clarifying the process for those in similar situations. The department strongly defended the decision, saying there had been no legal error by the official involved.

''Sadly, for many refugee children, it is not uncommon for a parent to be missing and presumed dead,'' Mr Townsend said after the court reserved its decision. ''We hope that this case will make clear what is required of visa applicants and help to get children out of dangerous war-torn countries more quickly and in a safe manner.''

Mr Tahiri, 19, was granted refugee status in 2009, is living in Dandenong and studying to be an accountant, but says he is consumed by concern about his mother and siblings, aged eight, 13, 16 and 17. ''It is hard to find meaning in my life when my family are not safe and are scared every day,'' he says.

''I really miss all of them. For the first year I couldn't really sleep and, even now, every night I see my family and my mum, it is like a nightmare that I have. I thought it would pass but it doesn't go away.''

Mr Tahiri says he is worried about the safety of his family in Quetta, where members of the Hazara ethnic minority live in fear, and it is too dangerous for his siblings to go to school.

''It gets harder and harder to talk to my family while I am waiting for there to be an answer on their case, but even if I don't speak to them my heart beats for them.'' This time last year, Victoria Legal Aid successfully challenged a decision by the department that denied another young Afghan refugee the chance to be reunited with his mother because he had turned 18 after arriving in Australia.

In a decision that enabled those who turned 18 after lodging claims to be reunited with immediate family members, a full bench of the court ruled that the government's construction of its legislation could lead to ''capricious and unjust'' results.