Charities fear they will become "ambulances at the bottom of the cliff" if coronavirus payments are cut off too soon.
The sector has seen a massive spike in demand during the pandemic, which followed the devastating summer bushfire crisis.
Demand at Foodbank Australia has spiked by 78 per cent in recent months, with the organisation now feeding 1.4 million people.
"We have a very real concern that we are not yet at the peak of food relief demand," chief executive Brianna Casey told a federal parliamentary inquiry on Wednesday.
Ms Casey said panic buying had severely impacted Foodbank's ability to feed vulnerable Australians.
She is also concerned about what will happen when the JobKeeper and JobSeeker support packages end in September.
Foodbank's concerns were echoed by UnitingCare Australia, St Vincent de Paul and the Australian Red Cross.
"We don't want to be the fleet of ambulances waiting at the bottom of that cliff," UnitingCare national director Claerwen Little told the inquiry.
"We want to be part of the team of construction workers building a fence at the top."
Vinnies has seen reduced demand during the pandemic from its usual clients.
Chief executive Toby O'Connor puts that down to social restrictions, fears about catching coronavirus and temporarily increased welfare payments.
But Vinnies has seen increased demand from new clients, including asylum seekers, international students and casual workers.
Mr O'Connor wants JobSeeker unemployment benefit payments to be permanently increased and has called on the federal government to develop a national social housing strategy.
Red Cross Australia director Noel Clement said his organisation had seen a massive rise in demand for help from temporary visa holders.
"We provided support to about 14,000 people over recent months compared to less than 1000 this time last year," he said.
A recent report found the coronavirus pandemic could force about one in six Australian charities to shut their doors within six months, leaving vulnerable people without vital services.
The pandemic could also prompt the loss of 200,000 jobs as the $155 billion sector cuts costs and charities close.
In April, the Morrison government announced an immediate $100 million funding injection for more than 300 charities and community organisations.
Families and Social Services Minister Anne Ruston said at the time a further $100 million would be allocated over the next six months as needed.