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.