The Department of Home Affairs is set to sign a contract to build a visa processing platform within days, but the public sector union is warning the plan could be as risky as the "robodebt" debacle.
Under a plan the department says will free up public servants to make more complex decisions, basic visa processing is set to be managed by a private provider that will build a software system to handle the millions of visas applied for each year.
While the department maintains government officials will always hold final decision-making power, the Community and Public Sector Union has argued this is only a technicality, and the plan does represent privatisation.
In a submission to a Senate inquiry the union showed that while the private provider wouldn't make the final decision on the visa, its algorithms would determine if a person's identity is verified, if they have health conditions, a partner or child and a satisfactory English level. The department would then make a decision based on that information.
For more sensitive information - like if a person had a criminal history, an Interpol Red notice or posed a threat to national security, the private provider would make an initial assessment before an application is forwarded to the National Character Consideration Centre.
"It is clear that the private provider will have immense discretion to determine who is issued a visa," said assistant national secretary Michael Tull.
"It is certainly privatisation."
Under a situation modelled by the union - a student visa - Mr Tull believes the department would only have a minimal role.
"It gives you the very clear sense that by the time a Home Affairs employee actually presses the button and authorises it, there's nothing left to do."
Mr Tull is also concerned that under the Migration Act, decisions made by computer programs are still considered decisions made by the relevant minister.
"It's a technical fiction," he told The Canberra Times, saying a decision could be made before it is seen by a public servant.
Mr Tull has told the committee Centrelink's issue with the "robodebt" system - where the agency's online compliance intervention averaged income across a 12 month period should be a cautionary tale for the visa system.
"Episodes like Robodebt diminish trust in government and democracy. A wise government would seek to avoid a Robodebt with visa and citizenship decisions," the submission said.
The Department has told the committee that while it has improved its processes in recent years, it is hampered by older computer systems that can't keep up with expectations.
"It is increasingly the case, however, that the opportunities to improve current legacy systems and processes are being exhausted and a step-change in capability and service delivery approach is required," Home Affairs' submission said.
"The Department is not handing over control of decision making," the department said.
"The Department alone will determine the business rules that govern what the Global Digital Platform does, which questions are asked of which applicant, which applications can be auto-granted in accordance with its business rules and threat profiles, and which applications need to be further considered by its officials."
Both the union and the department will appear before a Senate committee on Friday to give evidence about the visa system.