The Fair Work Ombudsman is alleging that four cleaners employed by subcontractors and contractors, working at Woolworths supermarkets, were underpaid more than $21,000.

The workers were employed at supermarkets at Deloraine, George Town, Riverside, and Mowbray.

The ombudsman will allege that the workers – including Korean nationals, some under 20 years of age – were paid flat rates of $14 to $15 an hour.

They were entitled to hourly rates of $22 to $23, plus penalty rates.

The ombudsman says their employer, Sung Gun Hwang and his company OzKorea Pty Ltd, provided false timesheets and pay sheets to Fair Work inspectors.

The underpaying is said to have occurred between January 2014 and January 2015.

OzKorea were, at the time, sub-contracted to provide cleaning services.

The ombudsman will also be proceeding against national cleaning company Pioneer Facility Services Pty Ltd, and its subsidiary, which formerly held cleaning contracts with Woolworths.

It will be alleged that the companies did not make an effort to check if OzKorea was paying its employees correctly.

There will be a directions hearing for Mr Hwang in Hobart in August.