A federal inquiry has heard families are abandoning their disabled children in order to fit into Australia's immigration criteria.

A parliamentary committee is looking at relaxing the rules which block many immigrants from entering Australia if a family member has a disability or a health condition.

Under the rules, families are blocked from entering Australia if a member has a disability or health condition predicted to cost taxpayers at least $20,000 over a lifetime.

The incoming chairman of the United Nations committee on the rights of disabled people, Professor Ron McCallum, is blind himself.

"I would not be allowed to emmigrate to this country even if I could assert that I could make a reasonable contribution," he said.

"I think that's outrageous."

He has told the inquiry the rules breach Australia's international commitments to human rights.

Meanwhile immigration law specialist from the University of Sydney, Professor Mary Crock, has told the inquiry some desperate families are leaving children behind in order to meet the criteria.

"There are families who will literally cast off a family member and it has had a horrendous impact on the child," she said.

Professor Crock says the system is inhumane and discriminatory, and people are being blocked even if they do not pose a cost to the economy.

Dr Dinesh Wadiwel from the National Ethnic Disability Alliance has told the inquiry some families assume they can bring their disabled children to Australia once they are settled there.

"Many families assume that once they get to Australia, it's going to be an easier task to be reunited with that family member," Dr Wadiwel said.

"Often they just assume because Australia's a fair and decent country that they'll be able to make that argument.

"Unfortunately, many families have to wait many years to be reunited and some never do."

The Human Rights Commission has also told the inquiry migrants' social contributions need to be assessed, not just their cost to the health system.