The Privacy Commissioner is investigating four complaints made by the Council of Trade Unions about the Ports of Auckland.
It comes as the company and the Maritime Union prepare to enter facilitation to try to end an eight-month dispute over the workers' collective contract.
The CTU on Friday confirmed it has made several complaints to the commissioner, including over the company releasing private details of a worker, Cecil Walker, to a right-wing blog.
Union president Helen Kelly says it has also complained about the release of another worker's ACC details to the same blog and comments made by a port representative to the National Business Review.
The ports company says it is not prepared to comment on the allegations, as it is a matter between the company and employees.
However, it says it will fully cooperate with any inquiry by Privacy Commissioner Marie Shroff.
The commission says it cannot make any comment at this stage.