Asylum seekers who were returned to Vietnam under Australia's boat turn-back policy have been punished with jail terms, a Melbourne-based Vietnamese advocacy group says.

During the election campaign the Federal Government trumpeted the return of a boat carrying 21 asylum seekers, intercepted en route to Australia.

It was the 28th boat to be turned back by Operation Sovereign Borders, which has now turned back 29 boats.

The Federal Government has previously said those turned back to Vietnam had been interviewed at sea, and it was found they were not owed protection because they were not facing political or religious persecution.

Voice Australia, a group that helps Vietnamese asylum seekers, has been in touch with a lawyer for two of the organisers of the ill-fated trip to Australia from Vietnam by boat, picked up in June.

Spokesman Trung Doan said a husband and wife who organised the trip but did not make a profit were facing respective minimum jail terms of one and seven years.

Mr Doan has also been in touch with relatives of those who were returned to Vietnam last year, on two separate boats, each carrying 46 people.

He said five asylum seekers from those boats were either in jail or facing jail terms, under Vietnamese law that makes it illegal to organise a trip to flee Vietnam.

"One of the men, I've been in touch with his wife, she said his legs have now become immobile, because of the conditions in the jail," Mr Doan said.

"He can't move he has to be in a wheelchair."

Mr Doan said while some of the asylum seekers were "economic refugees", others had fled because they were farmers who had their land confiscated were regularly interrogated by the authorities due to protests.

"They've been interrogated by authorities which really scared them and they wanted to leave," he said.

Air and sea patrols of Australia's northern waters are being increased in what the Government has called "ring of steel" to prevent people smuggling, after the announcement refugees on Manus Island and Nauru would be resettled in the United States.