First Union general secretary Dennis Maga says migrant employers exploiting their own people is rife in New Zealand and it is "killing legitimate businesses".
Dodgy employment practices are endemic to the food and hospitality industry, Mr Maga told Newshub, and he's particularly noticed Asian employers being exploitative.
"They recruit their own people, their own family, there are no employment agreements as a way to cut costs."
Mr Maga says while most businesses have regular health and safety checks, labour inspections are "seldom happening" in Auckland, Wellington and Christchurch.
He says migrant workers are in a precarious position where they endure poor working conditions based on a false promise of gaining a visa and a better life.
"They're promised sponsorship or a working visa, after three months working in these conditions."
After spending tens of thousands of dollars to come to New Zealand, migrant workers are scared to speak out and lose everything, Mr Maga says.
Employers will threaten to call Immigration New Zealand and have them deported "as a trap" to prevent them from contacting authorities or contacting their families.
First Union wants to see a special Government entity created to tackle migrant exploitation, saying that dealing with multiple agencies is a "stressful exercise" for unions and migrants.
The union works with Immigration New Zealand, the Ministry of Business, Immigration and Exports, and the Labour Inspectorate but would like to see a more simplified avenue for migrant exploitation complaints.
Mr Maga also wanted to see migrants attend a post-arrival seminar, which would inform them of their rights at work, how to access a union, and other settlement information they need to know.
Minister for Workplace Relations and Safety Iain Lees-Galloway told Parliament earlier this month the Government plans to launch an inquiry into migrant exploitation and double the number of labour inspectors in New Zealand.
"Exploitation is a source of human misery and is simply not acceptable in New Zealand. We need to be known as a nation that upholds workers' rights and a great place for migrants to live and work. The good employers should not be undermined by rogues who exploit their workers," he said.
A couple who own an Auckland-based restaurant were recently handed down the first custodial sentence for migrant exploitation in New Zealand, with one of them sentenced to 26 months in prison and the other to eight months home detention.