Crossbench MPs have warned the government they will use the balance of power in the lower house to push for a federal anti-corruption commission.

On Sunday Centre Alliance MP Rebekha Sharkie told ABC’s Insiders that “nobody should be above the law”, appearing to agree that an anti-corruption commission could investigate Australia’s spying on Timor-Leste during oil and gas treaty negotiations in 2004.

The warnings comes as MP Cathy McGowan has given notice of a bill to establish a national integrity commission and attorney general Christian Porter opened the door to discussing “all options” with the crossbench.

The Coalition government has never ruled out a push from Labor to establish an anti-corruption commission, but Porter has given a strong indication the government opposes the idea, saying there is no “persuasive evidence” that current methods of tackling corruption are insufficient.

Independent Kerryn Phelps’ win in the Wentworth byelection saw the government lose its majority in the lower house.

MP Andrew Wilkie told Insiders on Sunday that in the new hung parliament all six crossbench MPs “understand the need for an integrity commission or [independent commission against corruption], or something like that”.

Sharkie was asked about the prosecution of Witness K – the whistleblower who revealed spying by Australia – and his lawyer Bernard Collaery – and whether an anti-corruption commission would investigate an issue such as that.

Sharkie replied: “Nobody should be above the law, whether it happened back in 2004 or whether it happened this year, whether you are a politician, or whether you are a senior public servant.”

The member for Mayo said the crossbench had been pushing for an anti-corruption commission for “the best part of a year” because the Australian public need to have confidence that politicians “act with integrity” and are not above the law.

“And it’s just astonishing that we would not have [an anti-corruption body] given that we have that in every state.”

Wilkie said he was “firmly of the view” bugging Timor L’Este’s cabinet room was “not in accordance with Australian law”.

Wilkie reiterated crossbench demands to drop the prosecution of Witness K and Bernard Collaery, labelling them heroic whistleblowers. He noted that there had been no prosecution arising out of the “substantive matter” of spy agency Asio spying on a confidential joint venture negotiation.

Sharkie said the spying incident was “our Watergate and nobody is talking about it”.

While the comments keep the heat on the government over the Witness K prosecution, they may inflame political disagreements over the remit of an anti-corruption body.

The government is considering combining existing anti-corruption functions in law enforcement agencies, while Labor and the Coalition have publicly bickered over whether a new body would have jurisdiction to investigate former Liberal minister Bruce Billson and former Labor senator Sam Dastyari for various controversies.

On Saturday, Porter told Fairfax Media the government “continues to carefully consider the best way to further strengthen and improve the national integrity framework and I am open to discussing all policy options with members of the crossbench”.

“I would be very pleased to meet with any crossbenchers interested in the issue to discuss their views and the work conducted in this area by the government in considering ways to improve present integrity arrangements,” he reportedly said.

“It is important that changes in this area improve upon the current system, rather than adding complexity and confusion.”

“The experience at the state and territory level shows this is the worst area to engage in policy on the run.”

The Greens have had a bill before parliament since 2010 to establish a national integrity commission.

On Thursday Greens MP Adam Bandt predicted that Australia could have a new federal anti-corruption watchdog “by Christmas”, suggesting it was supported by majorities in both houses. Phelps agreed it was “very achievable”.

• The picture caption was amended on 1 November 2018 because those in the photograph are crossbench MPs, not independents as an earlier version said.