A union says Filipino immigrants working on the rebuilding of Canterbury are being exploited by their employers.
First Union says it knows of two cases where Filipinos were exploited, with some being made to work weekends without pay or not being paid for months at a time.
The first case relates to a subcontractor who made 40 employees work for free on Saturdays, although that matter has since been resolved.
The second case, which has not been resolved, involves 15 employees who say they have not been paid for six to 11 weeks' work.
Immigration Minister Michael Woodhouse says he is very concerned by the claims, but is confident that those heading to the region are given sufficient advice.