Big businesses are warning the Abbott government its plan to make the carbon tax repeal retrospective to 1 July 2014 – even if it has not passed the parliament – is a recipe for confusion and uncertainty and could be “unworkable”.

Labor and the Greens are insisting they will vote down the package of eight repeal bills in the Senate when parliament resumes on Monday and will do so again if they are returned to the parliament next year – leaving the fate of the legislation to the new Senate that sits from July 2014.

Business groups are urging the opposition parties to pass the repeal bills in the interests of certainty, but say that if the repeal remains unlegislated there are big problems with the government’s plan to deem that it has taken effect from 1 July anyway.

The aluminium industry – a major electricity user – has warned the government that if the repeal is not passed by September the idea of backdating it could be “unworkable”.

“The passage of the repeal legislation after 1 July 2014 becomes progressively more difficult to manage as parties continue to act in accordance with the [carbon pricing] scheme and … the array of actions unable to be unwound retrospectively grows progressively larger,” the Australian Aluminium Council said in a submission to a rapid Senate inquiry into the repeal.

“At some point, retrospective repeal will become unworkable. Notionally this period is … where the legislation has not passed before 1 September 2014. At this point it is the view of the AAC that a significantly different approach to that outlined in the draft repeal legislation would need to be employed.”

The power industry – generators, retailers, power networks and gas pipeline providers – is similarly alarmed. It said the government’s stated intention to backdate its repeal to 30 June 2014 “does not mean that businesses can ignore the carbon tax while it remains law”.

“The possibility of retrospective repeal, even for a short period, will create risk for all participants in the market and complicate the repeal process,” the organisations said in a joint submission.

Pacific Hydro urged the government to consider a “plan B” of abandoning the idea of retrospectivity if it can’t get its repeal through by 30 June.

“The prospect of a change being applied retrospectively to lawful contractual arrangements adds significant costs and risk to all participants in the market and adds markedly to the complexity of repealing the carbon legislation itself. We would strongly recommend the department, and the government, consider developing a plan B to enable an orderly, efficient, least-cost and lower risk approach to the carbon price repeal should a 30 June ‘end date’ not be delivered.”

The Minerals Council of Australia, and companies including Westpac, Santos and Caltex have also expressed concerned about how the “retrospective” repeal would work in practice.

If Labor and the Greens both stick to their position on the repeal, its fate is likely to be determined by Clive Palmer’s Palmer United party senators. PUP will have two, and possibly three, senators and has done a deal with the Victorian Motoring Enthusiast’s senator, Ricky Muir, to vote as a bloc. Palmer – whose Queensland Nickel refinery has more than $6m in outstanding carbon tax liability – has insisted companies should be absolved of their existing carbon tax bills. He has refused to state how his senators will vote on the repeal. Palmer himself, who is the member for Fairfax, abstained from the lower house vote.