The cause of Monday's power failure was a fire on the property of a farmer at Tamahere in Waikato.
More than 70,000 customers from Northland to Waikato were without power for about four hours.
Farmer Steve Meier has been in a land access dispute with Transpower for five years.
He says he warned Transpower time and again the trees needed trimming or the power might arc.
Transpower chief executive Patrick Strange told Morning Report that Transpower crews had been trying to get on Mr Meier's property for some time, but he had blocked their access.
Resumption of supply was delayed by about three hours.
Dr Strange acknowledged the company was aware of the risk to the lines from the trees but was unable to do anything about it.
He said the real solution was to build alternative transmission lines to Auckland.
Auckland City Mayor John Banks is demanding that Transpower be held accountable for the outage.
Mr Banks told Morning Report he does not believe that one angry farmer was able to shut down the entire power supply to Auckland.
However, Energy Minister Gerry Brownlee says it would have been helpful if Auckland City Council had supported the alternative Waikato power route into Auckland which has only just begun to be constructed.
Federated Farmers says it supports Mr Meier. Waikato president Stew Wadey says the fallout will affect Transpower's relationships with other farmers in similar situations.
He believes Transpower owes Mr Meier compensation.