Under the changes introduced to Parliament on Wednesday, those whose protection claims are rejected face return to their country of origin unless it is decided they are ''more likely than not'' to suffer significant harm.

Immigration Minister Scott Morrison says the existing threshold, where they are not returned if there is a ''real chance'' of them suffering harm, means they can stay if this risk is ''as low as 10 per cent''.

The new ''more likely than not'' test would mean there would have to be a ''greater than 50 per cent chance'' of a person suffering significant harm for them not to be returned, he said.

The change covers those seeking protection under international treaties against torture and on civil and political rights.

The higher threshold is one of many sweeping changes to the Migration Act, which will require asylum seekers to provide ‘‘sufficient evidence’’ for identification to receive a protection visa and will not give automatic protection visas to family members of a visa holder.

If the changes are passed, they will apply to all asylum seekers whose claims are processed in Australia, which includes plane arrivals and the around 30,000 people who have not been sent to Nauru or Manus Island because they arrived before the PNG arrangement in July.

Determinations on sending people back to their country would be made if asylum seekers’ claims for refugee status are rejected, a spokesman for Mr Morrison said.

Mr Morrison defended the changes, saying the government remains committed to ensuring it abides by its international obligations, despite substantially increasing the risk threshold.

‘‘This is an acceptable position which is open to Australia under international law and reflects the government’s interpretation of Australia’s obligations,’’ he said.

‘‘This Bill deserves the support of all parties. We need the tools to ensure public confidence in Australia’s capacity to assess claims for asylum in the interests of this country, and against the interests of those who show bad faith. These changes uphold the importance of integrity in the establishment of identity, and increased efficiency in our protection processing system,’’ he said.

But human rights lawyers are shocked at the changes, saying they are ‘‘very significant’’.

‘‘These amendments would allow the government to send people back to their country of origin even if there’s a 49 per cent chance they’ll be killed or tortured as soon as they get off the plane,’’ said Daniel Webb, director of the Human Rights Law Centre.

‘‘We shouldn’t even contemplate breaching international law by returning people to such high risks of serious harm, especially at a time of unprecedented global need.’’

Greens spokeswoman Sarah Hanson-Young said it was an ideological and dangerous attack on vulnerable asylum seekers already in Australia.

“If you can’t prove that you are more likely to be shot than not, then you will be on your way home.’’

Labor immigration spokesman Richard Marles said the changes were troubling.

“We would be extremely concerned if the government attempts to use complex legislation to sneak through shifting the goal posts on what determines refugee status,” he said.

with Michael Gordon