Most of New Zealand's 106,000 international students are on student visas allowing them to work a maximum of 20 hours a week.
But Luo, NZISA's equity vice-president, said many worked long hours "under the table", not realising that it was against the law.
"We can't work on a freelance basis on a student visa, but many students, because they pay so much fees in New Zealand and are in financial difficulty, are trying to take up jobs and doing things that are not allowed."
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Kristen said the association knew of students being exploited in Auckland, Wellington, Otago and Waikato.
"We've had issues in Waikato where international students get paid $10 an hour, they get forced into 12-hour work shifts, that is in the agriculture sector," he said.
"In Wellington we have worked with a few students, writing to the employer to let them know, and if that doesn't produce any results we are helping the students to contact the labour inspectors.
"But even myself as a law student don't know how to go about that process, so it's really hard for an international student whose second language is English."
The association plans to hold its first conference in Wellington on September 8.