Eleven Auckland restaurants, which form part of the Masala food chain, have been fined a total of $66,000 for failing to provide documents about staff.
Restaurant bosses were asked for contracts, wage records, and holiday and leave records for about 100 workers.
The deadlines for submitting the documents were in May and June, but they actually arrived in August.
The Employment Relations Authority said it asked for the documents after complaints from several staff members.
It said a number of the Masala workers were recent migrants, who were part of a particularly vulnerable section of the workforce.
Labour Inspectorate Northern Regional Manager David Milne said if employers did not keep such records, it was almost certain that staff were not getting their entitlements.
"There's also another factor in terms of the employer failing to meet maybe requirements in the health and safety space or indeed taxation requirements," he said.
"An employer who is failing to meet requirements in the money area will generally be failing to meet their requirements in another part."
The Masala group was also under further scrutiny, Mr Milne said.
"We're currently investigating Masala on some other matters, so there are some live penalty actions at the moment, and we have a significant case at the moment that we're currently working on.
"So the situation with Masala is far from completed."
Communities needed to come forward about employers they believed could be exploiting workers, Mr Milne said.
The eleven restaurant operators have been ordered to pay $6000 each, plus costs, although Mr Milne said three of them had since gone into liquidation.
But Service and Food Workers Union representative Chas Muir said the fines would not deter worker exploitation.
"It's only $6000 per company. When you consider if you can sell food at New Zealand prices and slash your labour costs by underpaying your workers and getting them to work very long hours, it's a pretty lucrative incentive to keep that going," he said.