The Unite Union is accusing supervisors of been bullying union members working at Auckland International Airport's food court.
The union has organised a series of short strikes during the past few weeks, over what it says is New Zealand's worst employment contract.
It says workers have no guaranteed hours, and can be rostered on for ten days in a row without consultation.
Unite national director Mike Treen says a complaint has been filed with the Employment Relations Authority, claiming supervisors have broken the law by denying workers shifts and telling them they will not get promotions unless they leave the union.
Mr Treen says the company, HMSC-AIAL Ltd, has ignored numerous complaints and emails about the alleged harassment.
The company, which runs most the airport's food outlets, says it does not discriminate based on union membership.
General manager Anne Singe says the union sent it emails about harassment during the week, but could not prove the allegations.
She says the company knows nothing about the details of the union's complaint.