Powerful senator Rex Patrick has abandoned negotiations with the coalition on environment law reforms over a fight about wage subsidy transparency.
The South Australian independent is waging a fierce campaign to force companies turning over more than $10 million to reveal JobKeeper payments.
The Morrison government's refusal to disclose the information has cost it a key upper house vote on changes to speed up environmental approvals for major projects.
Senator Patrick argues the two issues are related because both relate to ethical business practices.
"I'm really frustrated with this. This is the biggest public expenditure failure in the history of the Commonwealth," he told Sky News on Monday.
"It is not OK to give away taxpayers' money to wealthy investors and individuals."
Political and media pressure has led to some profitable firms handing back JobKeeper payments with Harvey Norman returning $6 million last week.
Senator Patrick said the government's refusal to put more transparency around the scheme raised questions over whether environmental approvals would be ethical.
"It tells me I shouldn't be working with them on other legislation that requires good ethics and the right balance between the needs of businesses and the needs of the environment."
The Morrison government now needs support from either Jacqui Lambie or Stirling Griff - also both independents - to secure the bill's passage through the Senate.
Proposed changes to Environment Protection and Biodiversity Conservation Act would create a one-touch approval system which hands greater approval powers to states and territories.
More than $13 billion in JobKeeper flowed to companies that increased revenues.
The federal government argues the scheme's design was necessary to pump money into businesses at the start of the pandemic.