The research, commissioned by union E Tū, recorded the experiences of mostly Filipino, construction workers in Christchurch and Auckland in 2017 and 2018.
Most experienced pay discrimination, with some earning as low as $19 an hour, compared to $35 paid to Kiwi workers.
Many workers also experienced damp and unhealthy living conditions.
Three of the workers interviewed shared a sleepout with another 10 in the house, all paying $150 a week. Another example involved four families sharing a four-bedroom home.
There was also wide-spread exploitation of migrants by immigration companies and "so-called" pastoral care companies, researcher Catriona MacLennan said.
"Many workers were in debt to immigration companies when they arrived, while others were being gouged by companies providing services such as a car or internet access.
"Most complained their pay was too low to meet immigration criteria for extended or permanent working visas or residency."
E Tū industry co-ordinator engineering and infrastructure Ron Angel said for the first time there was research showing Filipino migrant workers being underpaid for no other reason than their ethnicity.
"When I was reading this, it nearly brought me to tears.
"The angst they were going through, and the suffering on a daily basis, being away from their families.
"What got me was, here we were welcoming these people into New Zealand to help rebuild Canterbury and we didn't look after them.
"In fact, we made life terrible for them and I feel ashamed."
The issue of expensive, unhealthy housing also needed to be dealt with.
"If you're going to decide you need migrant workers, then there needs to be reasonable housing for them.
"You can't just bring them in and throw them into anything you can find."
The report made recommendations for Government action, to ensure newcomers were properly supported and got necessary advice.
"If Immigration NZ wants these workers here, then it needs to provide that pastoral care," Angel said.
