Pregnant asylum seekers in offshore detention are typically brought to the mainland to give birth, but changes to the Migration Act last year mean that people who arrived in Australia by boat after July 19, 2013 are classed ‘‘unauthorised maritime arrivals’’ and can be removed offshore. The law is silent on such asylum seekers’ babies who are born in Australia.

Greens Senator Sarah Hanson-Young said that she would write to every MP on Wednesday seeking their support for the bill as an ‘‘issue of conscience’’. She plans to introduce the bill when Parliament resumes in May.

‘‘We are, by incarcerating these newborn babies, creating the next damaged generation . . . we know the damage the detention of children has (on them),’’ she said. ‘‘If we allow this to continue, we are knowingly destroying them,’’ she said. ‘‘I don’t think that’s a political issue, it’s a moral issue.’’

Senator Hanson-Young said that she had learned from workers on Nauru and Christmas Island that the Abbott government last week sent four babies born in Darwin to Nauru. They were the youngest asylum seeker children to be transferred offshore, ranging from two to eight months’ old, she said.

She feared for their safety, with ‘‘primitive’’ medical facilities on the island-nation, and about 1000 asylum seekers forced to share four toilet blocks in detention: ‘‘The camp is in the middle of an (operating) phosphate mine. It’s dusty . . . there’s seven to eight families in each tent. That’s no way to be able to look after a child, let alone a newborn baby.’’

About 18 pregnant asylum seekers on Nauru were also due to give birth in coming months, she said.

Senator Hanson-Young blamed a spike in the number of women and children arriving in Australia by boat on the Coalition’s cut to humanitarian intake and ban on family reunion visas.

She said members of the Coalition, Labor and those on the cross-benches struggled with the current policies: ‘‘No one finds it easy to try to justify the way (children are) being treated.’’

Immigration and Border Protection minister Scott Morrison would not confirm or deny reports of asylum seeker babies being sent to Nauru. He said: “The Greens simply refuse to acknowledge that the policies being implemented by the Government are stopping the boats and stopping the deaths at sea.”

The Greens’ proposal comes before a High Court case regarding ‘‘Baby Ferouz’’, a baby born in detention in Brisbane, which will determine the legal status of such babies.

Maurice Blackburn principal Jacob Varghese said on Tuesday that a number of asylum seeker parents had since contacted the firm from Christmas Island, seeking legal assistance to prevent their children from being sent to Nauru or Manus Island. Two of the 26 babies were born in Melbourne.

Mr Varghese wrote to Mr Morrison on Monday asking for a written undertaking that he would not remove the families until after Baby Ferouz’s case had been decided, by 4pm on Wednesday.

‘‘We’re very hopeful the Minister will see the sense of this undertaking . . . But if the Minister doesn’t give that undertaking we will be contemplating appropriate legal action,’’ he said.

He said that the government had no lawful authority to take the babies to Nauru or Manus Island because they did not arrive by boat, but were born in Australia.

Mr Varghese said it was unknown when the High Court case would be heard.

He acknowledged that the Federal Government could still change the law, even if the challenge was successful: ‘‘If they want to make an argument in Parliament that babies should be locked up from the day they’re born, then let Parliament debate that and let Parliament decide it.’’

Mr Morrison said that he was aware of the letter but said: ‘“As this issue is being considered by the High Court it is not appropriate to say anything further at this point.’’