South Australian workers would still be able to claim compensation for multiple injuries caused in the same incident, under legislation proposed by the state government after backing down due to pressure from unions.

However, the threshold for workers to be considered "seriously injured" would increase from 30 per cent to 35 per cent of whole-person impairment in order to keep down the premiums employers pay to ReturnToWorkSA to cover potential work injury claims. 

The opposition has not formed a position on the proposed laws but described the government's moves to fix the ReturnToWorkSA scheme over the past two weeks as "a complete shambles".

Seriously injured workers can receive compensation until retirement age rather than for two years.

The government had been worried a judgement last year that workers could claim multiple injuries from the same accident — including, for example, a physical and a psychological injury — could increase the amount employers pay to ReturnToWorkSA from 1.8 per cent of their wage bill to 2.2 per cent.

It introduced legislation on the same day as the state budget that would have forced workers to claim for their injuries separately, sparking surprise and anger from unions.

Premier Peter Malinauskas said under the agreement today, premiums were expected to increase to 1.9 per cent, after negotiations with both unions and business groups.

He said the government planned to introduce the new bill to parliament tomorrow and he hoped it would pass both houses by the end of next week.

Workers would continue to be able to claim multiple injuries at once.

"It is our hope now that a broad agreement has been reached between both unions and business, that we can now enjoy the support of the upper house and I would certainly hope that [Opposition Leader] David Speirs would come to the party and provide Liberal Party support for this legislation so this can be dealt with," Mr Malinauskas said.

Under the proposed legislation, seriously injured workers would be able to claim a lump-sum payment rather than weekly payments from ReturnToWorkSA.

Unions and businesses respond

SA Unions secretary Dale Beasley called the bill "certainly not perfect" but a lot better than the previous legislation he described as "astounding".

He criticised how the government had handled the issue three months into being in power.

"Hopefully the government, when we come up against challenges like these in the future, will open a dialogue far earlier and hopefully before legislation is put on the table.

"However, workers are in a far better situation than they were a fortnight ago."

Business SA chief executive Martin Haese said businesses had already suffered "extreme disruption" due to the COVID-19 pandemic and did not need more expenses.

"What we on behalf of the business community in South Australia do not want to see is a pronounced increase in ReturnToWorkSA premiums, so a lower premium for employers in this extremely uncertain environment is a better premium," he said.

"Notwithstanding, we respect the rights of workers, we want workers to be safe.

"Of course, we do now call upon the Leader of the Opposition, David Speirs, to work collaboratively with the Premier to forge an outcome which works with business and preserves a sustainable cost base across all employers in South Australia."

Opposition highly critical of process

The Liberal party room met this morning to discuss the previous legislation — offering its support — but Mr Speirs said they could not vote on the new proposal because all they had seen was "one sheet of dot points".

"Business isn't clear what the liability will be going forward, whether that is actually affordable by business and but also by the ReturnToWorkSA scheme," he said.

"So this is getting very complicated very quickly.

"What this probably needs is a serious investigation by an independent figure."

He said Mr Malinauskas thought of himself as a "Bob Hawke-like negotiator" when the process had been "a complete shambles".

"It's quite ridiculous, really."

If the government does not gain the support of the Liberal Party, it would need votes from members of two of the three minor parties in the Legislative Council: the Greens, SA Best and One Nation.