The federal opposition is trying to get the government on board with changes to its wage subsidy bill, which has been introduced to parliament on Wednesday.

The bill extends JobKeeper to March 2021, splits it into a two-tiered system for full-time and part-time workersand outlines what companies can do if they're no longer eligible.

Firms remaining on JobKeeper 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.

In that instance, they can reduce a workers' hours to 60 per cent of what it was prior to the pandemic.

Labor's industrial relations spokesman Tony Burke says workers could therefore lose up to 40 per cent of their wage, which would amount to $300 a week for someone on minimum wage.

He wants the government to consider a safety net provision so a worker can't have their hours reduced to the point they're paid below the JobKeeper rate.

"We can't be agreeing to change the industrial relations system to allow people who at this time have been struggling already through the pandemic ... to then face further cuts because the business they work for is doing better," he told parliament.

Extending the program to March takes the total cost of JobKeeper to more than $100 billion.

"The phasing down of the JobKeeper payment will ensure a smooth and gradual transition to economic recovery," Treasurer Josh Frydenberg said as he introduced the bill.

Shadow treasurer Jim Chalmers is worried scores of workers still can't qualify for the scheme, such as casuals and university and aviation staff.

The rate of the scheme is up to Mr Frydenberg and Labor hopes he aligns the payments with the current state of the economy.

"We need him to get that right," Mr Chalmers said.

A review of the initial laws found anomalies in the way it operated.

Labor will support the legislation even if the party's concerns about employers cutting working hours aren't addressed.

The Morrison government plans to cut the wage subsidy from $1500 to $1200 a fortnight at the end of September and then to $1000 from December to March, for full-time workers.

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

Meanwhile, Tasmanian workers without sick leave will receive access to a $1500 pandemic leave payment to help them through their 14-day self-isolation.

Australian Associated Press