The workplace watchdog has confirmed it is investigating Rockpool Dining Group over union claims the company doctored timesheets in Melbourne and Sydney to avoid fully paying workers for hours they worked.

Key points: The group has been accused of retrospectively changing timesheets to avoid paying employees for their full hours

The group has been accused of retrospectively changing timesheets to avoid paying employees for their full hours Former Rockpool chef Rohit Karki alleged he was forced to sleep at work between 20-hour shifts and was paid $12 an hour

Former Rockpool chef Rohit Karki alleged he was forced to sleep at work between 20-hour shifts and was paid $12 an hour In a statement, the group said the latest underpayment allegations had been made "without any substantiation"

It comes after Maurice Blackburn lawyers lodged a complaint with the Fair Work Ombudsman on behalf of United Voice's Hospo Voice union, alleging Rockpool tampered with timesheets to cover up underpaying staff.

United Voice Victoria secretary Ben Redford told ABC Radio Melbourne that lawyers had estimated Rockpool could owe workers more than $10 million in back pay.

"It could be the biggest case we've seen of wage theft in the hospitality industry," he said.

Mr Redford said staff members would clock in and out using a fingerprint scanner, but he alleged some staff had witnessed managers changing the recorded times.

"People were working 70 to 80 hour weeks [but] have records showing they … only worked 38.5 hours," he said.

Mr Redford said the union would be requesting electronic records of timesheet data from Rockpool Dining Group to prove the allegations.

Rockpool business includes the Rockpool Bar and Grill venues in Melbourne, Sydney and Perth. ( Supplied: Rockpool Dining Group )

In a statement, the company said it was engaged with the Fair Work Ombudsman directly and had only found out about the latest allegations through the media.

"These allegations have been made without any substantiation," the statement said.

"RDG [Rockpool Dining Group] has no evidence to substantiate claims of group-wide manipulation or destruction of data in order to intentionally underpay employees."

In a brief statement, the Fair Work Ombudsman said it was investigating the alleged breaches of the Fair Work Act regarding three unidentified employees.

Australian celebrity chef Neil Perry is the face of Rockpool Dining Group, but has not been personally accused of doctoring timesheets. ( Supplied: Rockpool Dining Group )

The Fair Work Ombudsman's investigation comes as a former chef in mediation with Rockpool alleged he was forced to sleep in the kitchen in between 20-hour shifts.

Hospo Voice member Rohit Karki entered individual mediation with the group today after filing a court application claiming he was owed upwards of $100,000 in backpay.

"I worked close to 80 hours [per week] with no breaks. They didn't keep records of people doing extra hours," Mr Karki told ABC Radio Melbourne on Friday.

He said Rockpool Dining Group would "authorise timesheets … in line with the contract and authorise it regardless of the hours staff actually worked".

Mr Karki said he began working at Rockpool Melbourne in 2012 and claimed he worked a "crazy" number of hours without adequate pay and was isolated from other staff members.

A statement from Hospo Voice also claimed Mr Karki was forced to sleep on a pastry bench between 20-hour shifts and worked consecutive days without breaks for $12 an hour.