Scott Morrison and Josh Frydenberg have played down the significance of remaining approvals for the controversial Adani coalmine, characterising the outstanding determinations as “sub-approvals” and “minor” matters, and insisting the government will make decisions based on science.

With some Queensland Liberals and Nationals escalating an internal campaign for the remaining Adani sign-offs to be done this week, before Morrison heads to the polls, Liberals in the southern states are now bracing themselves for the federal approvals to be granted some time this week, even though that timing is inconvenient because it will kickstart third-party activist campaigns against the Coalition.

Labor has warned the government against making any major decisions on the controversial project only days before an election is called, but with sections of the LNP now engaged in internal strong-arming there is a view inside the government that the outstanding groundwater approvals are now more likely to happen pre-election than not.

A federal sign-off would be politically inconvenient for Frydenberg, who faces a challenge in his seat from Oliver Yates, an independent campaigning on climate change, and Julian Burnside, a high-profile lawyer running for the Greens, amplified by a GetUp campaign.

In an attempt to minimise the growing controversy, the treasurer told reporters on Monday the major approvals for Adani had already been granted, and the remaining decisions were “sub-approvals”.

Morrison – who was interrupted by rolling anti-Adani protests during a lunchtime event in Brisbane on Monday – also moved earlier in the day to characterise the outstanding determinations as “quite minor” and then refused to say whether the government would finalise the processes or not. “We are taking the advice from scientists like we have in the past.

“There are some remaining administrative manners and we are following the normal process and taking the advice of the scientists when it comes to making those decisions – I do not think there is anything particularly unique about these remaining matters.

“They are quite minor in the scheme of the broader approvals provided already and, like in all the other cases, we will be relying on the scientific evidence provided to the government in making those decisions.”

The Labor leader, Bill Shorten, also campaigning in Brisbane, seized on the government’s internal battle. He declared the government was in “meltdown” over approvals for Adani.

Shorten referenced a report in the Courier Mail saying the Liberal senator James McGrath had threatened to issue a press release calling for the resignation of the environment minister, Melissa Price, “if she did not fix a problem she created by attempting a deliberate go-slow on the [Adani] project”.

“LNP politicians are bullying the minister for the environment, saying you will lose your job and the government, if you don’t give us the answer we want on Adani,” Shorten said.

“This is a failure of ethics in government at the highest level. It highlights the chaos and division within the government. A government which is broken. They can’t agree on anything.

“Why on earth don’t we have a national anti-corruption commission, because that is not the appropriate use of political influence, to threaten [Price’s] job as environment minister, unless you do as you’re told?”

The outstanding groundwater approval is not the only hold up with the mine, with Adani’s management plan for the endangered black-throated finch, which is found in the mine’s proposed location, also needing a signoff.

The Queensland state Labor government has ordered a review of the black-throated finch management plan, which delayed the project further, with the Queensland resources investment commissioner saying the approval process for the mine could now take up to another two years.

Even if the commonwealth deals with its remaining regulatory matters this week, the groundwater plan also needs state approval, and that won’t occur before the federal election.

Shorten, who has also faced difficulties about Labor’s position on Adani, was pressed by reporters about Labor would do about the project should it win the election in May.

The Labor leader said he would be “guided by the best science and by the law of the land, and we’ve won’t be ripping up any contracts”.

Asked what he would do in the event the federal approvals were granted this week, Shorten hedged. “It’s hard to predict what they’ll do in the next six hours. Are you sure they’ll give federal approvals? We don’t know.”

The shadow climate change minister, Mark Butler, on Saturday repeated his personal opposition to the controversial coal project. Butler told Guardian Australia: “I don’t think there’s a case for opening up a new thermal coal mine.”