Unions will launch High Court action against Qantas over allegations the airline manipulated rosters to pocket some of its wage subsidy payments.
A December court ruling found in favour of the Qantas interpretation of JobKeeper, overturning an earlier decision backing unions.
The full Federal Court found the airline is allowed to use penalty rates paid in arrears to offset the amount of wage subsidies directly passed to employees.
But unions want workers to receive the JobKeeper payment as well as the full value of overtime and other penalties even if they are stood down.
A Qantas spokeswoman said all employees were paid at least $1500 a fortnight during the first stage of JobKeeper and then the reduced minimums specified by the government.
"The unions are again wasting their members' money and our money on continuing this legal action during the middle of a crisis," she said on Wednesday.
"The court found we are administering JobKeeper as the government intended and we have always made JobKeeper payments according to advice from the Australian Tax Office."
The airline also rejected claims of roster manipulation.
"Rostering arrangements during the stand down period was done in consultation with unions," the spokeswoman said.
ACTU Secretary Sally McManus said the unions' stance was about ensuring justice for workers.
"Qantas is forcing workers to work public holidays, weekends and overtime and then effectively denying them overtime and other penalties they have earned," she said.
"Workers are standing up to Qantas over this injustice and will take the case all the way to the High Court."
Business groups have raised concerns about back payments if unions win the case on behalf of workers.
The ACTU, Transport Workers' Union, Flight Attendants' Association of Australia and Australian Services Union will seek special leave to appeal last year's ruling.
Flight Attendants' Association secretary Teri O'Toole said Qantas workers were struggling on basic JobKeeper, which was recently reduced to $1200 a fortnight.
"They have spent public holidays and weekends away from their families and they should be paid fairly. They should not have to go to court to receive the pay that they have worked for," she said.
"After years of loyal service and helping Qantas through tough times when it was in financial dire straits, workers feel very let down by the airline."
