The council considered them to be temporary signs on private land that contravened provisions of clause three of the Signs Control Bylaw 2005.
The clause states, among other things, that no person shall paint, erect or leave standing or lying any sign in a public place or any temporary sign on private land.
The dispute became more heated when council chief executive Mark Simpson was accused of bullying Northern Advocate columnist Nickie Muir, after she wrote a column critical of him.
Mr May empathised with Ms Muir and started displaying signs calling for Mr Simpson to stand down. Mr Simpson was cleared of any wrongdoing, but Mr May persisted with the signs and displayed them on his truck along with others. On January 21, the council seized Mr May's truck from Okara Drive.
Mr May claims the warrants presented by council enforcement officers to seize his Isuzu truck were unlawful as they were unsigned and not dated.
The truck is worth $1500 and the council's costs of impounding it stood at $3270 as at July 30.
The council is prepared to return the truck upon payment by Mr May of its costs but he is refusing to pay and has vowed to fight the matter in court, saying the council's actions in seizing his truck may be unlawful under the Bill of Rights Act.
The Whangarei District Court will hear the case next month.
Mr May stood for election as a councillor this month and erected billboards as part of the election campaign which were critical of Mr Simpson.