The case involving Chinese construction workers caught in bonded labour by a recruitment company is just the "tip of the iceberg", a Chinese building industry chief says.

Forty-eight Chinese workers signed contracts with recruitment firm National Personnel Ltd, and claim to have paid between $40,000 and $55,000 to be brought into the country by a man named Peter Li.

They have been issued trespass notices from the firm, which also owns the property they occupy, and claim their passports, food and bedding have been taken by representatives of the company.

"I think the reported issue here is just the tip of the iceberg," said Frank Xu, president of the NZ Chinese Building Industry Association.

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"There are many more cases like these but victims are afraid to speak up and whistle blow for fear of losing their jobs and income to support their family back home and have their visas revoked."

Xu is calling on the community and government agencies to protect their rights and help these migrant workers "get through this difficult and highly stressful time".

The association is urging migrant workers to sign up to its week-long training programme aimed at helping workers settle into New Zealand's building sites, which includes educating them on their rights, legal frameworks and health and safety.

Xu said there was an urgent need to run an awareness campaign - both here and in China - on the rights of workers and how to look for recruiters.

"In many cases, scammers work professionally and may appear to be legitimate and victims may not be aware until they arrive into New Zealand," Xu said.

He says what is needed is a certification programme of legitimate employers and the provision of a hotline where victims can call for help.

Unite Union is helping the workers and is calling for public help to accommodate 23 of the evicted workers.

Immigration New Zealand is investigating and the recruitment firm is helping with inquiries.