The Unite Union has filed legal action against fast food chain Burger King with the Employment Relations Authority in Auckland.
It alleges the company carried out a secret campaign to encourage employees to resign from the union.
The union's statement to the court also accuses the company of setting progress targets for achieved union resignations.
The union says it is seeking hundreds of thousands of dollars in penalties against the company as well as individual managers and area managers for what it calls breaches of workers' rights.
Unite says Burger King is carrying out an anti-union campaign to cover up the worst examples of exploitation of vulnerable, young and migrant workers at a major employer in this country.
The company is yet to comment.