Malcolm Turnbull has defended the "common sense" decision to delay a sitting of federal parliament's lower house as Labor and crossbench MPs ramp up pressure on the government over the deferral.
The prime minister insisted parliament had to deal with same-sex marriage and MPs' citizenship disclosures before the end of the year.
"It makes sense, just common sense, to in effect move the two weeks of the house sittings forward a week," Mr Turnbull told reporters in Sydney on Tuesday.
"That gives us the time to complete that important work."
But crossbench MP Andrew Wilkie says the federal parliament has a "moral imperative" to sit next week as Turnbull government ministers line up to defend deferring the lower house session.
Labor has drafted a letter petitioning Mr Turnbull to reverse his decision to postpone the House of Representatives sitting to December 4.
Victorian independent Cathy McGowan has confirmed she will not take part in any protest sitting, but her four crossbench colleagues are expected to co-sign Labor's letter.
Their support would mean 73 MPs support the push - the same number the government has on the floor of the house with Barnaby Joyce and John Alexander off fighting by-elections.
"With numbers being that close surely there's a moral imperative if not a legal imperative on the prime minister agreeing that the parliament would sit next week," Mr Wilkie told ABC Radio.
Leader of the House Christopher Pyne said the delay would give the Senate time to pass the same-sex marriage bill and allow parliament to sort out the dual citizenship mess.
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However, the announcement came just hours after Queensland LNP senator Barry O'Sullivan said up to four coalition MPs were considering breaking coalition ranks to vote for an inquiry into the banks.
Mr Pyne insisted the decision to delay the return of parliament had nothing to do with thwarting Labor or rogue government backbenchers mustering the necessary votes to launch an investigation into the banks.
"There's no motion or bill to establish a banking royal commission either before the Senate or the House of Representatives," he told ABC radio.
Treasurer Scott Morrison also played down the link but Opposition Leader Bill Shorten grabbed it with both hands.
"There is no doubt in my mind that one of the reasons why Mr Turnbull has cancelled parliament next week is because he knows a banking royal commission is inevitable," Mr Shorten said.
"And he will do everything he can do to protect his mates at the top end of town."
'We haven't ruled anything in or out'
The opposition has cooled on its initial declaration that all of its MPs would be turning up for work in Canberra on Monday, regardless of the government's decision.
"We haven't ruled anything in or out yet but certainly the shadow cabinet meeting is definitely on. The broader caucus is something we're still working through and still consulting on," Manager of Opposition Business Tony Burke told ABC radio.
"If the only reason for going was for the purpose of a media conference, then we wouldn't do it."
Mr Pyne said Labor's "political stunt" would cost $787,000.
Mr Wilkie doesn't want taxpayers to foot the bill for a shadow cabinet meeting which he believes could wait until the following week or be done over the phone.
