The Council of Trade Unions says the Ports of Auckland has admitted leaking personal details about an employee who spoke out against the port.
The employment records of wharf worker Cecil Walker were leaked to blogger Cameron Slater in March, who published it on his Whale Oil website.
Mr Walker was given nearly 21 weeks off work in 2007 and 2008 on full pay as his wife was terminally ill.
President of the Council of Trade Unions Helen Kelly told Radio New Zealand a letter from chief executive Tony Gibson to the Maritime Union acknowledged the port was behind the leak.
Ms Kelly said the letter does not name who was responsible for the leak, but it did state the leak was a response to Mr Walker speaking out publicly against the port.
"They acknowledge they released it. They explain, in their terms, why they released it, and regardless of the fact they clearly agree that it probably breached the Privacy Act, that's implied in the letter.
But they don't go on to say that they change, in fact they go on to say that they reserve the right to do it again."
Mr Walker had spoken out over the difficulties of juggling family life and work and the further impact casual hours would have.
Ms Kelly said the letter argued the information was released as it showed how family-friendly the port was an employer.
She said the information was released to keep port workers from speaking out.
"Employers collect private information about their employees, they do that for their business, they're allowed to collect it and store it. The law requires them to keep that private. And basically they fired a shot at these workers to try and shut them up."