An estimated six million Australians will receive the money but some unions say up to 2.2 million workers have been left out of the JobKeeper scheme.
The ACTU says it's not compulsory for employers to implement the JobKeeper program.
But employers who do sign up will be obliged to pass on the funds to staff as a wage subsidy - however employees could still be working some hours while receiving the payment.
All full-time and part-time workers are eligible, along with casuals who have a 12-month link to their employer, sole traders and New Zealanders on 444 visas.