According to the union, on average, each worker will receive almost $11,000 in back pay. One worker is set to receive more than $145,000.

You won’t believe this, but I found it in the OP’s article. Wild. Also:

“The primary underpayment that we first uncovered related to misclassification, so workers being paid in many cases level one in the retail award when, in fact, they should have been paid level three, four or five,” Mr Peak said.

"For some workers, that represented up $5 an hour that they were being paid below the legal minimum.

“It also went to the mis-payment [sic] of a range of allowances [such as] not being paid cold work allowances, not being paid the uniform allowance, or uniforms weren’t being provided to them as they should be under the award.”