A box of petroleum products going on an aircraft undocumented, passenger stairs being wheeled away before the plane door was closed and collisions with refuelling hoses were detailed in memos sent to Swissport cargo workers in the past six months, the Transport Workers Union said on Tuesday.

Swissport is one of the companies Qantas outsourced its ground-handling work to in 2020, when it sacked about 1700 baggage handlers.

“This is urgent. We want the air safety regulator to investigate. We want to make sure our skies are safe,” TWU secretary Michael Kaine said on Tuesday.

“We would rather sound the alarm than, in the event of a catastrophic event, be accused of remaining silent.

“We need to leave no stone unturned to bust open Qantas’ ground-handling contracts to the bare bones and examine the commercial pressures piled onto a chronically understaffed, inexperienced workforce.”

“This is a disaster waiting to happen.”

According to a “dossier of highly concerning safety breaches” released by the TWU, several memos acknowledged understaffing as a safety issue.

“The business is acutely aware that our human resource levels are simply not at a sustainable level to meet the ongoing demand from the airlines,” one reads.

Another notes “an increase of incidents where firearms have been incorrectly offloaded onto the arrival’s carousel, rather than delivered to Baggage Services … effectively allowing anyone to pick the item up and walk away.”

A third outlines how workers failed to close the rear cargo door of a Boeing 737 after loading was completed.

“The consequences could have been severe had the engineer not picked up on the error,” Swissport told workers.

The union’s release follows an ABC Four Corners report on Monday detailing Qantas workers’ concerns that the airline’s reputation for safety is at risk.

In a statement, Qantas said it made tough decisions during the pandemic that were ultimately about ensuring the airline avoided the fate of numerous legacy carriers around the world, protecting many thousands of jobs.

The airline operated in one of the most closely scrutinised industries and would never compromise on safety, it said.

“It’s worth noting that Four Corners did not contact the Civil Aviation Safety Authority regarding any claims made in the program,” Qantas said.

“CASA has since reiterated that it has confidence that Qantas is operating safely.”

Federal government MP Bill Shorten on Tuesday ruled out nationalising Qantas, but said the airline had treated staff badly.

“They wielded the axe too hard. It’s a blind spot for them,” he told Nine’s Today Show.

“I used to be a union rep where we used to look after the engineers there, so I think they’re a bit hardline on their own workforce.”

Swissport has been contacted for comment.