Immigration New Zealand denies slashing the number of compliance checks it makes on employers who take on migrant workers.
Labour immigration spokesperson Darien Fenton has issued figures showing visits to employers in the horticulture and viticulture industries nearly halved in the past three years, from 484 to 251 last year.
Ms Fenton says checks have been slashed, and migrant workers need to have their legal rights protected.
However, Immigration NZ general manager Peter Elms said the number of visits in 2009 was higher than usual because of an increased focus on educating employers.
He said checks in the past two years are consistent with previous years.
Mr Elms said employers who exploit migrant labour will not be tolerated.