THE Australian Greens have rejected emphatically a Government move to legalise the offshore processing of asylum seekers.

Prime Minister Julia Gillard has announced the Government next week will introduce to parliament changes to the Migration Act following the High Court's recent decision to rule unlawful a swap deal with Malaysia.

"The prime minister is wrong, she is seriously wrong," Greens leader Bob Brown said in Canberra today.

"We won't support this legislation, nor we will support the coalition's amendments, whatever they might be."

He warned the major parties were developing an "unholy alliance" as Labor moved to the right on the issue.

Greens immigration spokesperson Sarah Hanson-Young said the current discussion on processing refugees was reminiscent of 10 years ago when John Howard was prime minister.

"This Government is copying and, in fact, going even further than John Howard and (and former immigration minister) Phil Ruddock did in 2001."