Mr Shorten says key questions remain unanswered after a $1.2 billion settlement between Robodebt victims and the federal government was reached in 2020.

"The Robodebt campaign over four years was the government going to war with its own people and it didn't have the legal authority," he told reporters.

The automated matching of tax and Centrelink data to raise debts against welfare recipients for money the coalition claimed to have overpaid was ruled unlawful in 2019.

But the government has never detailed who was accountable for the scheme and which ministers knew of its problems.

Mr Morrison was social services minister when it was conceived but has denied personal responsibility for the disaster.

Labor has long called for a royal commission into Robodebt, which Opposition Leader Anthony Albanese describes as "a human tragedy, wrought by this government".

"Against all evidence and all the outcry, the government insisted on using algorithms instead of people to pursue debt recovery against Australians who in many cases had no debt to pay," he said on Saturday.

"It caused untold misery. Only an Albanese Labor government will find out the truth."

The Australian Council of Social Service is backing the plan, calling it appropriate and proportionate.

"We need to properly probe the decisions and processes that led to this woeful situation and make sure nothing remotely similar ever happens again," CEO Cassandra Goldie said.

"We also need to probe the underlying thinking."

The royal commission would be tasked with establishing who was responsible for the scheme, what advice was used in its implementation and complaints handling processes.

It would also look at the cost to taxpayers of the debacle and harm caused to those targeted.

Labor says the royal commission has $30 million budgeted against it and the terms of reference would be in place before Christmas if it forms government in May.

The prime minister hit back at the proposal, saying the issues had already been addressed.

"There have been numerous inquiries into this and there have been court matters which we fully co-operated in," Mr Morrison said.

"Almost $750 million in reimbursements have been made by the government and the changes to the scheme have been put in place. The problem has been addressed."

Any inquiry would need to start with the process of income assessment, averaging of incomes, which was introduced by the Labor Party, Mr Morrison said.

"I find it quite hypocritical that a scheme the Labor Party actually introduced for income averaging in assessing people's welfare entitlements, that they now seek to criticise the government for," he said.

"The Labor Party do this all the time. They just come out and make these assertions."

But Mr Shorten said Australians still did not know "how this reckless scheme was unleashed".

"We do not know whether poor legal advice was given or whether legal advice was simply never sought," he said.

"We do not know if public servants were inappropriately heavied and politicised. And without knowing the true origins we do not know what safeguards could be put in place to prevent a repeat."

Labor will also launch a user audit of the myGov government services digital portal to assess its reliability and functionality.

Australian Associated Press