Malcolm Turnbull's claim that his planned ban on refugees processed offshore from ever visiting Australia does not breach international law has been challenged by the United Nation's refugee agency.

The agency's regional representative, Thomas Albrecht, has told Fairfax Media the ban appeared to be in breach of Article 31 of the Refugee Convention, which prohibits refugees being penalised for seeking protection in an irregular manner.

The Prime Minister has challenged Labor to back the ban when Parliament resumes on Monday, though neither the opposition nor the UNHCR has yet been shown the draft legislation. Labor leader Bill Shorten has labelled the ban "ridiculous".

Pressed on whether the ban was in breach of Article 31 of the convention, Mr Turnbull has said: "We have taken legal advice and we are satisfied it is within power and consistent with our international obligations."