The federal government is looking to continue pandemic-inspired emergency powers and JobKeeper for another six months beyond September.

Firms remaining on the scheme will still have the power to change employees' hours, duties or work location.

Others booted off JobKeeper will also retain the capacity to change conditions if they prove a 10 per cent reduction in turnover compared to the same period last year.

That so-called "legacy" cohort won't be able to reduce hours by more than 60 per cent and will be banned from directing employees to work less than two hours a day.

Labor is investigating whether it would be easier for legacy businesses to reduce workers' hours than those of employees who have never received JobKeeper.

It's understood the issue is a live question within the opposition as it weighs up what amendments it may attempt to make to the bill.

But even if proposed changes are sunk, the opposition will support the legislation, which is due to be introduced to federal parliament on Wednesday.

Labor MPs also raised concerns at Tuesday's caucus meeting over branches of struggling businesses missing out on JobKeeper because other arms of the company were not eligible.

Industrial Relations Minister Christian Porter said the flexible arrangements had saved hundreds of thousands of jobs during the pandemic.

"The worst possible thing that you can do to a struggling business is to force it to pay staff to do work that doesn't exist because of COVID-19," he told parliament on Tuesday.

Mr Porter said while there were potentially 3.5 million workers covered under the measures, just 667 disputes had been lodged with the Fair Work Commission.

He said the system was safeguarded by a test ensuring the employee could not be usefully employed for normal days or hours because of coronavirus-linked issues.

The Morrison government plans to cut JobKeeper payments from $1500 to $1200 per fortnight at the end of September, and then to $1000 from December to March.

Treasurer Josh Frydenberg is responsible for setting the rate, meaning that change won't need to be legislated.

Labor wants JobKeeper to remain at $1500 for another six months with Victoria's coronavirus lockdown smashing the national economy.

"We want to make sure that low-paid workers aren't missing out and aren't going to have their already low wages slashed substantially under this legislation," leader Anthony Albanese told ABC radio.

Australian Associated Press