Another popular Melbourne restaurant chain has been hit by claims it has underpaid its staff, and one former worker alleges he was told his "job was on the line" and others were fired after they asked to be paid award rates.

Former workers say twenty ex-employees have been paid about $150,000 after raising the allegations with the Ichi Group, which runs popular Melbourne restaurants including Fitzroy's Ichi Ni Nana and St Kilda's Ichi Ni.

The United Voice union said at least some casual workers employed by Ichi Group were paid just $18 per hour — approximately $5 less than the award rate at the time.

The union, which represents workers across the nation, has made a complaint to the Fair Work Ombudsman claiming Ichi Group also did not pay employees penalties or overtime rates.

It has requested an investigation into the organisation's past and current pay arrangements.

The ABC contacted the Ichi Group by phone and in writing, but has been told the company would not comment.

'Overworked and underpaid'

James Lea started working at Ichi Group's Fitzroy restaurant complex, in Brunswick Street, in March 2016.

After working for $18.50 per hour for around seven months, Mr Lea requested his pay be increased to the award rate, he said.

"Their response was to sit me down in the office and tell me I was doing a bad job and my job was on the line," he said.

"They weren't able to give me a pay rise because they were unhappy with my progress."

Mr Lea said he had initially been looking forward to working at an exciting venue on a street he loved.

A sign for Ichi Ni NaNa restaurant on Brunswick Street in Fitzroy. ( ABC News: Billy Draper )

"The whole time I was there, I was underpaid. When I left after 18 months … myself and a few other friends got together … and collectively signed a letter requesting that they investigate whether they'd paid us correctly."

Mr Lea said he received more than $13,000 in backpay from Ichi Group, but said the signatories who were still employed subsequently lost their jobs.

Mr Lea said bar staff sometimes worked up to 17 hours without a break, and others would sometimes wait at the venue for hours only to find they weren't required.

He said payslips didn't accurately reflect hours worked, or weren't even given to workers.

'Entrenched culture in Melbourne hospo'

United Voice said every Ichi Group worker it spoke to was being ripped off, but it was even more alarmed by the widespread exploitation of workers on temporary visas, who were paid as little as $18 per hour with no penalty rates.

"Very few of them have felt confident to speak up — anonymously or privately — because the threat to their visa and the threat to their jobs," Mr Lea said.

"They were paid for a 38-hour week, but often doing 50 to 60 hours. Often students were forced into lower rates of pay and cash-in-hand because the business refuses to pay the proper casual entitlements."

Oscar Shaw, who has joined an action to recover allegedly unpaid wages from Melbourne's Ichi Group restaurant chain. ( Supplied: United Voice )

Former employee Oscar Shaw, who also signed the letter demanding repayment, said there are other workers who could be owed money.

"I have no doubt that everyone who has ever worked for them is owed money. We're currently helping a second group of people claim back probably around $60,000," Mr Shaw said.

"There is an entrenched culture in Melbourne hospo of underpayment.

"The sad thing is many workers accept this as unchangeable.

"Those who are able to earn a decent wage look back on previous poor wages as a sort of necessary part of the career."

But Mr Lea said he was part of a great team, despite the working conditions.

"The staff all tend to bond together, especially in the face of adversity. The owners of the business would always tell us we were one big family … one of the things that made us laugh was that bond was in spite of them," Mr Lea said.

"The 20 of us who came forward was just a tiny fraction of people who have worked at the venue over the past years.

"Hopefully from now the Ichi Group will investigate these claims properly and thoroughly."