The new guidelines for the JobKeeper extension will begin on September 28 with more businesses and workers will now qualify for the government payments with these updates.

Treasurer Josh Frydenberg has announced businesses will only need to show that their GST turnover had fallen over one quarter, instead of multiple, to be eligible for the scheme's extension.

Workers will also qualify if they were employed on July 1, rather than March 1.

The initial JobKeeper will finish on September 28, with businesses and employees needing to apply for the extension.

The Government initially outlined the JobKeeper extension guidelines on July 21, but says it needs to extend its criteria after the Victoria Government implemented stricter lockdowns across the state.

Under the previous guidelines, a business needed to record a loss in the June and September quarters.

Mr Frydenberg has blamed the stage 4 restrictions in Melbourne, and the wider restrictions across Victoria, for the Federal Government changing the scheme's extension.

"The combined effect of the economic deterioration in Victoria, which will see more firms needing to rely on JobKeeper, and the changes we are making to the program, will see the cost of JobKeeper increase by around $15.6 billion," he said.

"The introduction of stage 4 restrictions by the Victorian Government will have a severe economic impact on the Victorian and Australian economy."

The changes will also affect businesses who will apply for the second extension of JobKeeper. The second extension will begin on January 4 next year.

Under the previous guidelines, a business would have needed to record an actual GST turnover loss for the June, September and December quarters of this year.

Mr Frydenberg said a business would now need to show a loss for only the December quarter to qualify for the scheme in January.

These guidelines also affect non-profit organisations.

Shadow Treasurer Jim Chalmers said the changes were a "step in the right direction".

"To the extent that they've relaxed some of the eligibility criteria, that's a welcome step. But there are other things which trouble us in the changes that the Government announced," he said.

"And we still remain concerned that a lot of people are still left out of JobKeeper."

Prime Minister Scott Morrison described the revised guidelines as "doing whatever it takes".

"Our response is to get the right support to all those Australian families, workers and businesses that need us, as these circumstances change," Mr Morrison said.

"This means more support for more workers and more businesses for longer, as we battle this latest Victorian wave."

Employee eligibility will also be extended, with a worker qualifying for payments if they have been with their workplace since at least July 1, instead of the March 1 deadline initially slated.

New employees will be eligible for JobKeeper payments dating back to August 3.