The Vietnamese community has urged the Australian Government to protect a group of asylum seekers it has reportedly sent back to Vietnam.

The Victorian president of the Vietnamese Community in Australia, Bon Nguyen, said on Sunday he had been told at least some of the 42 Vietnamese asylum seekers intercepted off the coast of Western Australia last week arrived back in Vietnam overnight.

"Just because on the track record of the Vietnamese Communist regime of what they do to the people trying to escape the regime," Mr Nguyen said.

"I have a great fear for their safety.

"If [the] Australian Government has returned them back to Vietnam already, please have some sort of monitor program so that our Australian embassies in Vietnam can actually keep an eye on them."

Greens senator Sarah Hanson-Young said the Government had broken international law in returning the asylum seekers back into danger.

The Refugee Convention prohibits the return of people to a place where their life or freedom may be threatened on account of religious, racial, social or political factors.

Senator Hanson-Young said asylum seekers returned by Australia earlier this year were facing persecution.

"Many of those people have been imprisoned, children have been banned from going to school and a number of them have been punished as a result of trying to flee Vietnam as asylum seekers," she said.

"It's a breach of international law and it flies in the face of the refugee convention."

The Government has refused to say whether or not it has returned the asylum seekers.