Conservatives are flexing their muscle ahead of the opening of the 45th parliament, with government MPs warning explicitly that marriage equality is dead without a plebiscite, and the push to overhaul the Racial Discrimination Act gathering pace.

After Nick Xenophon on Monday confirmed his NXT Senate bloc would vote against the marriage equality plebiscite, effectively killing the proposal, given Labor is widely expected to follow suit, the prime minister was congratulated during the Coalition party room meeting by conservative MP Andrew Hastie, who declared marriage equality would only happen with a plebiscite.

Hastie told the meeting he wanted to publicly congratulate Malcolm Turnbull and moderate frontbencher Simon Birmingham for holding the line and making clear that the plebiscite was the only means for achieving marriage equality in this term of parliament.

“Same-sex marriage has one pathway in this party going forward and that is through the plebiscite,” Hastie told the meeting.

Outside the party room, South Australian Liberal senator Cory Bernardi was seen walking the corridors collecting signatures for his private members bill which seeks to wind back some of the protections under the section 18C of the Racial Discrimination Act. It’s understood Bernardi currently has support from at least half a dozen Coalition colleagues.

After a challenging couple of months post-election, the prime minister attempted to steady the government’s political fortunes and use the opening party room meeting of the new parliament to flag the importance of budget repair, confirming the government will bring forward an “omnibus” savings bill later this week.

Turnbull raised the rhetorical stakes in the party room, describing budget repair as “a fundamental moral challenge”.

The government entered the opening week without producing the legislation for the omnibus savings bill, but on Monday evening, the treasurer’s office moved to brief Labor and crossbenchers about the contents of the bill.

The bill has 24 savings measures and the proposals add up to savings of $6.1bn, according to a backbench briefing note seen by Guardian Australia on Monday night.

The government will move to introduce the bill at this stage on Wednesday, but it cannot be debated this week because it wasn’t produced with sufficient time for Labor to consider it at its caucus meeting on Monday.

Strong internal debate is continuing in Labor over whether the opposition should support some of the measures in the omnibus legislation, including a proposed cut to pensions and Newstart, courtesy of the abolition of an energy supplement – a saving worth $1.4bn over four years.

A meeting of the left caucus in Canberra on Monday was dominated by concerns from MPs about axing the energy supplement, which impacts people living below the poverty line, and two additional measures – a $1.3bn saving Labor has booked from abolishing the Australian Renewable Energy Agency, and a potential cut to children’s dental programs.

The debate didn’t spill into caucus because the legislation was not available for caucus consideration earlier in the day.

The backbench briefing note makes it clear the abolition of the energy supplement needs to happen during the spring session of parliament, because the schedules take effect in March and July 2017.

Bill Shorten is attempting to shrug off his internal concerns by pushing ahead with efforts to pressure the government on a banking royal commission, including proceeding with procedural motions in the House of Representatives later this week designed to maintain pressure for the inquiry.

While the major parties laid the ground for the sitting week, which begins Tuesday with the ceremonial opening of proceedings, the political day was dominated by discussion about the marriage equality plebiscite.

The debate began to build last week, with the Labor leader Bill Shorten sending a strong hint Labor would block the plebiscite – a move that prompted Liberal MPs to begin their warnings to Labor that it it would be the plebiscite to resolve the issue, or it would be nothing.

On Friday the Greens announced they would block the plebiscite, citing the harm to vulnerable LGBTI people from divisive debate and polling suggesting the LGBTI community would be prepared to delay the reform if it meant avoiding the plebiscite.

All or nothing warnings from Liberals escalated on Monday. Birmingham, the education minister, a leading moderate and a longtime supporter of marriage equality, said there was no prospect of a parliamentary vote this term if the plebiscite was killed in the parliament.

The binary nature of the debate is worrying some progressives. Former Greens leader Bob Brown argued in an interview with the Conversation that while a plebiscite was the wrong way to go to resolve the issue, without it “I think that down the line there’s three more years of waiting”.

The Greens new education, finance and trade spokeswoman, Sarah Hanson-Young, also signalled she had concerns about the Greens decision to block the plebiscite. She told Sky News she could “see the arguments on both sides”, including those “that desperately want to see marriage equality become a reality”.

“The last thing I want to see is politicians, particularly those that are determined to destroy the campaign for equality win.

“I don’t want to see this issue pushed off to the never-never.”