Malcolm Turnbull has weighed into the debate over Bill Shorten's citizenship, saying the Labor leader is "prepared to cover up anything".
However a senior cabinet colleague says he doesn't believe Mr Shorten is a dual citizen.
The opposition leader says he has no issues with his citizenship but has declined to release paperwork showing he renounced his British ties prior to the 2007 election.
Mr Shorten has labelled talk of his potential ineligibility for parliament a "crazy conspiracy" without any evidence to back it up.
"Transparency is not Bill's long suit," Mr Turnbull told reporters in Albury on Thursday.
"It's up to him whether he wants to be transparent and disclose the basis on which he says he renounced his citizenship. He is creating a big issue by failing to do so."
Mr Turnbull said the unions royal commission showed how Mr Shorten, as secretary of the Australian Workers Union, traded away workers' rights and sought to fund his own election campaign.
"If he is prepared to cover that up, he is prepared to cover up anything," Mr Turnbull said.
Cabinet minister Mathias Cormann said every member of parliament needed to make their own judgement about their personal circumstances.
"I don't believe that Bill Shorten is a dual citizen," he told Sky News.
"I'm not going to give public advice to members of other parties as to how they should handle this."
