Labor’s policy on the contentious robodebt scheme is “not clear”, welfare campaigners have said, despite the opposition repeatedly using the program to attack the Coalition.

Responding to a question from older voter about the rate of Newstart on Monday, Bill Shorten told the ABC’s Q&A program that “when it comes to a woman on $265 a week” the government’s position was “we better check that and send her a robodebt letter from Centrelink”.

Labor’s human services spokesman, Ed Husic, also lashed the scheme as “shabbily conceived and managed” in February as Melbourne woman Madeleine Masterton launched a federal court challenge.

The government has come under intense criticism over the value and ethics of the scheme. The program forces past and current welfare recipients to prove they were not overpaid while they were receiving income support.

Though it has made a series of administrative changes aimed at blunting its harshest aspects, the government remains committed to the program.

But the opposition is yet to reveal how a Shorten government would deal with a program forecast to recoup about $3bn for the budget.

Husic did not respond to multiple requests for comment about the opposition’s position on the program.

Lyndsey Jackson, who founded the NotMyDebt campaign, said Labor’s current position was “not clear”.

“We’ve certainly been happy to the extent that [the shadow social services minister] Linda Burney has advocated for the voice of people that have been affected, there were obviously Labor senators involved in the Senate inquiry and contributed to the report. Those things are positive,” Jackson said.

“However, despite of all of that, despite the evidence and the stories, it is not clear that they will stop the program or what changes, if any, they will actually make.

“Really what we want to hear is that this program is going to be stopped, that getting this stuff right is more important than a budget bottom line.”

In 2017, a Labor-Greens majority Senate inquiry recommended the scheme be suspended and for all debts calculated using the error-prone “income averaging” process to be reassessed.

Asked about Labor’s position, the chief executive of the Australian Council of Social Services, Cassandra Goldie, acknowledged the opposition’s involvement in that inquiry.

Goldie noted Labor had been “critical” of the program and said it had promised to waive debts for domestic violence where they were accrued through coercion.

But she added that the peak body wanted both major parties to give a “firm commitment to abolish robodebt, and replace it with a fair and humane system of debt recovery”.

“We also need the next government to investigate what has happened to people who have already been badly affected by the unleashing of this automated nightmare,” she said. “Over 150,000 people have paid debts without a review, so we do not know how many of those debts were correct, or how many people just paid them because they could not fight them.”

The Greens senator Rachel Siewert, who chaired an inquiry into the program, described robodebt as “an abuse of power” and called on Labor to back its abolition.

Critics, including Victoria Legal Aid, which is supporting Masteron’s legal challenge, argue the “opaque” way Centrelink calculates alleged overpayments is unlawful.

It involves comparing a person’s income reported to the tax office against the income they reported fortnightly to Centrelink.

Robodebt scheme costs government almost as much as it recovers Read more

Guardian Australia revealed on Sunday the Department of Human Services is arguing Masterton’s case can no longer proceed after it dropped her debt.

Before the Coalition ramped up the automated debt matching process, public servants manually oversaw the process.

Goldie said there continued to be a “range of serious problems with robodebt”, including “the use of averaging which is leading to inaccurate debts and the reversal of the onus of proof”.

In February, new data revealed that Centrelink that had wiped, reduced or written off 70,000 of the 409,572 debts raised.