He said vehicle restoration was allowed under the council's district plan, and his work on them was "a hobby, not a business".
But neighbours were concerned the cars were a safety hazard that attracted vermin, and affected property values, and the council applied for an enforcement order.
In their judgement, Judge Jon Jackson and commissioners Owen Borlase and John Mills said there were grounds for the enforcement order under the Resource Management Act.
The relevant section allowed action where, in the opinion of the court, an activity was "likely to be noxious, dangerous, offensive, or objectionable to such an extent that it has or is likely to have an adverse effect on the environment".
The order required Mr Osborne to remove 11 vehicles by November 10 and a further six by March 14.
The ruling said the court "urges Mr Osborne to take these enforcement orders seriously".
"He should be aware that if he does not comply with the orders the council may undertake the works and then seek to recover the costs from him."
That would mean, at best, having to pay the council's costs, and "worse, having to sell the property to pay these costs".
Mr Osborne was not at home when the Otago Daily Times called yesterday.