At least eight regional airlines could collapse within days because of the crippling coronavirus pandemic, putting life-saving flights at risk.
Regional Express Airlines (Rex) has also warned it could shut down without immediate support from local, state and federal governments.
Opposition transport spokeswoman Catherine King said the federal government's aviation relief package, worth up to $715 million, was not nearly enough and failed to support airlines whose fleets were grounded.
Rex deputy chairman John Sharp said the smaller airlines were effectively offering the government a 24-hour ultimatum.
His airline transported blood and even COVID-19 test samples between the regions and capital cities.
"This may no longer be possible in the foreseeable future," he said.
"It would be most ironic if (Nationals leader and Deputy Prime Minister Michael McCormack) should be presiding over the collapse of all these regional carriers under his watch."
He said moves by the consumer watchdog allowing airlines to coordinate flights and the aviation watchdog's easing of regulatory burdens had helped.
"However, these measures alone will not allow the airlines to survive the next three months," Mr Sharp said.
Mr McCormack didn't rule out further financial help, saying he had been in regular contact with the airlines industry.
"I acknowledge calls for further support and am working closely with industry in responding to this crisis," he told AAP.
"Our first priority as a government is the public health and safety of Australians. This core focus underpins every decision we are taking in response to this crisis."
A joint letter from eight regional airlines urged the government to provide support, saying that unlike Australia's major carriers they were family or privately owned.
The airlines said any financial relief needed to go straight into airlines' pockets to keep them going.
"The government, while repeatedly proclaiming the importance of protecting regional aviation as a vital resource for growing the economy appears, instead, to have wiped its hand of the industry at what is its most critical time," the letter said.
It said the smaller carriers provided services to regions unattractive to the bigger airlines.
"The financial survival of our companies can be counted in days rather than weeks," the letter said.
Ms King warned aviation workers had no guarantee they would still have a job once the coronavirus pandemic was over.
Australian Associated Press
