Under the establishing legislation, Auckland Council Investments - the council holding company that owns Ports of Auckland - was required to bring a commercial governance to assets, he said.
"If for instance the target had been 6 per cent ... I don't think we would have seen different strategies because our role is to maximise the value of these investments ... so why would we have been satisfied with just merely a 6 per cent return."
Maritime Union president Garry Parsloe said the 12 per cent return on equity target was a figure pulled out of nowhere.
"There isn't a terminal in the world that gets 12 per cent," Parsloe said.
"I don't mind how much they get but not on the backs and the misery of those workers.
"The port is there to service the city of Auckland. It creates employment, it creates work in factories ... and it returns so much money into Auckland ... it's returning 6.3 per cent, it's doing everything it should be doing."
Swift said one of the first things Auckland Council Investments looked at was the port's results and returns.
"We ... didn't think these returns were adequate so we made a number of new appointments to the board, as directors retired, of people that we thought could bring innovation and change to the way in which the company was operating."
The labour dispute was an operational matter for the port, Swift said.
"Obviously because of its seriousness we are taking a close interest in it but we're certainly not driving the strategy, we're not telling them what to do and how to act."
Auckland Council Investments had other investments to look after including a 22.4 per cent stake in Auckland Airport, a film studio in Waitakere and a diversified investment portfolio.
"We've got confidence that the Ports of Auckland board are going to deliver the [12 per cent return on equity] result that we're looking for."