Samoan national Joseph Matamata, 65, also known as Viliamu Samu, is facing a total of 24 charges in relation to bringing 13 people from Samoa to New Zealand for horticultural work across Hawke's Bay.
Matamata, who has New Zealand residency and lives in Hastings, was arrested in December 2018 after a two-year investigation by Police and Immigration New Zealand.
He was originally facing 18 charges involving 10 people, but further charges were laid in August last year.
At the time of his arrest, Immigration claimed the case was a "new low for New Zealand". It said he confiscated migrants' passports, subjected them to assaults and threats and underpaid them.
Each slavery charge carries a maximum penalty of 14 years in prison while the human trafficking charges carry a maximum penalty of 20 years in prison or a $500,000 fine.
The trial is set down for five weeks.