The allegations are part of an investigation of the business by the Fair Work Ombudsman, which has discovered 59 employees of the popular carwash were short-changed almost $118,000 in wages.
One worker, a Korean 457 visa-holder who was employed as a cook, is alleged to have been forced to pay back her boss between $111 and $715 a week in cash from her wages, depending on the hours she worked.
Her annual salary was $49,333 and, after paying back a portion of her wages, Fair Work estimates she was being paid between $15 and $18.50 an hour.
The scam is alleged to have effectively stripped the cook of entitlements to overtime and weekend penalty rates under the Vehicle Manufacturing, Repair, Services and Retail Award. It is also alleged to have short-changed her of the minimum wage under the award.
The Korean national says she felt 'compelled' to pay the boss or risk her losing his sponsorship of her Australian work visa.
The Fair Work Ombudsman claims that, including the cash-back arrangement which led to $21,600 of her wages going back to her boss, the Korean national was underpaid a total of $29,587 over the 19 months.
The Ombudsman says she was one of 59 workers at Expresso's Southport and Labrador sites who were allegedly underpaid more than $147,000.
The casuals are said to have been paid flat rates of between $12 and $17 an hour, well below the $16.37 to $23.69 an hour specified in the award, and between $25.28 and $44.96 with penalties.
The Expresso business is operated by Ausinko Pty Ltd, a company controlled by Richard Sang Kyun Kim.
Kim, along with Ausinko manager Chao 'Tommy'Liu, are facing Federal Court action over the allegations.
Fair Work will allege that Ausinko implemented the cash-back scheme to make it look as though it was complying with the award.
Ausinko has given a commitment to repay the workers in full, and has paid back more than half of the underpayments.
However, it still faces a directions hearing of the Federal Circuit Court in Brisbane on August 1,
Fair Work Ombudsman Natalie James says court action was instigated because Ausinko has previously been put on notice over matters of employee entitlements.
She says this matter is of particular concern because it involves vulnerable workers.
Ausinko could face penalties of up to $51,000 for each contravention, while Kim and Liu face maximum penalties of up to $10,200 per contravention
The Fair Work Ombudsman is also seeking a court order for an external audit of Ausinko's pay practices next year.
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