A Chinese noodle bar chain is facing legal action for allegedly underpaying its staff by more than $600,000.

The Fair Work Ombudsman accuses W.X.Z. Enterprises of underpaying six workers at four of its stores in NSW and Queensland.

Court documents allege the company paid its Chinese workers a flat weekly wage of as low as $530 between July 2010 and March 2013.

The staff generally worked up to seven days a week and often more than 60 hours a week, it is alleged.

The ombudsman is seeking penalties and back-payment to the employees, who the agency says are owed $642,311.

One of the workers, who was a 457 visa holder and a cook at a Dubbo restaurant in regional NSW, was allegedly underpaid almost $190,000.

An investigation was launched into the business after the ombudsman received complaints from staff.

W.X.Z Enterprises faces penalties of up to $51,000 per contravention and its two managers could each face penalties up to $10,200 per breach.