An emergency hearing over the Qantas dispute has been told the only decision to be made is whether to suspend or terminate industrial action.
Qantas says 447 flights have been cancelled, leaving at least 68,000 passengers stranded worldwide since Saturday afternoon when the airline grounded its entire fleet.
The Fair Work Australia tribunal began a hearing over the clash between Qantas and three unions representing engineers, baggage and catering staff and long-haul pilots at 2pm AEST on Sunday.
Lawyers for the unions have asked Qantas executives how long they have been planning the shutdown and how they came to the decision.
Federal Government lawyers have implored both parties to focus on the issue at hand, saying the industrial umpire only needs to determine whether industrial action would be suspended or terminated altogether.
Earlier, a senior Qantas executive told the hearing that the airline was forced to ground its entire fleet for safety reasons.
The airline will lock out thousands of employees from Monday night.
The ABC reports that a Qantas executive, Lyell Strambi, has told Sunday's hearing that the aviation safety regulator had raised concerns about the airline's operations.
He said the long-running industrial action had resulted in a gradual increase in safety risks.
Mr Strambi said he took the decision to ground the airline's fleet after chief executive Alan Joyce decided the airline would take protected industrial action in the form of a lockout.
He said, based on advice he had received, it would be unsafe for the airline to continue operating during a 72-hour notice period before the lockout because of concerns regarding fatigue and distraction among staff.
Lawyers for the unions challenged that reasoning, saying airline executives were not qualified to say how their employees would react.
The Transport Workers Union federal secretary Tony Sheldon said the actions of Qantas' Chief Executive Alan Joyce will wreak havoc on the Australian economy.
Mr Joyce said the decision to ground the airline was only taken when unions ramped up their rhetoric after shareholders voted to give him a pay rise at Qantas' annual general meeting on Friday.