Labor has accused the federal government of botching its $130 billion JobKeeper scheme after more than a million fewer workers signed up than has been budgeted for.

The opposition and unions renewed calls for the scheme to be expanded after 4.7 million workers from about 728,000 businesses signed up – despite the scheme being budgeted to cover six million employees.

The fortnightly payments of $1500 per eligible worker started flowing on Wednesday.

But shadow treasurer Jim Chalmers accused the government of botching a good idea.

“When the Treasurer says this project is coming in under budget, what he really means is that it is too hard for too many businesses and too many workers to access the scheme itself,” he said.

“What the Treasurer doesn’t seem to recognise is the longer the unemployment queues get during this crisis, the longer it will take Australia to recover.”

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Temporary migrant workers and casuals who have worked for their employer for less than 12 months are among those excluded from JobKeeper.

But Australian Council of Trade Unions secretary Sally McManus said it appeared there would be money left over from the scheme, and it could be expanded.

“The Morrison government has no excuse not to expand eligibility to cover workers who have been left out and need support,” she said.

Ms McManus said the program excluded a quarter of the arts and entertainment industry, many casuals, contractors and visa workers.

“[This] is inflicting unnecessary economic hardship on millions of Australian workers and their families,” she said.

“The Treasurer can make this change immediately and should do so.”

Treasurer Josh Frydenberg was adamant the program would not be expanded, and said he expected more businesses to sign up in coming days.

“We’ve been pretty clear about the broad parameters of the program and that’s where it’s staying,” he told Sky News.

But since announcing the scheme, the Morrison government has made some changes. On May 1, it excluded employees from “sovereign entities” – companies owned by other governments.

That meant more than 5500 staff from aviation services company dnata, owned by the government of Dubai, became ineligible. Some of the devastated employees – who were previously told they would be eligible – had worked for Qantas for decades before the airline’s catering business was sold to dnata two years ago.

“We just all feel that that is wrong,” one dnata worker, who did not want to be named, told news.com.au.

“We pay our taxes, we are Australians.”

Mr Frydenberg said it was not clear how much would be spent on JobKeeper. But the government was likely to bank any savings if it was undersubscribed.

“The actual final number will be totalled up and spelt out at budget, no doubt, as part of our broader economic costings and forecasts,” he said.

“It is a significant amount of money already that has been committed across the economy.”

-with AAP