It is not every day that the ambassador from a country with which New Zealand has one of its best relationships is hauled into the Ministry of Foreign Affairs for a stern ticking-off.
Yesterday's decision by Foreign Affairs Minister Murray McCully to summon the Japanese ambassador to the ministry so it could formally reiterate New Zealand's unhappiness with a Japanese whaling support vessel entering New Zealand's exclusive economic zone is towards the stronger end of diplomatic responses.
It is certainly a step up from last Friday's demand that the embassy's deputy head of mission go to the ministry to be told of New Zealand's displeasure.
Moreover, the Government is not ruling out even firmer action, such as summoning the ambassador to the Beehive for a face-to-face dressing-down from McCully himself should there be another such incident. That would place New Zealand's reaction to the incursion into its economic zone on a par with its response to French nuclear testing at Mururoa Atoll in the mid-1990s.
The scale of the response and McCully's strong language denouncing the incursion seems to be driven by two factors.
First, the Japanese whalers deliberately ignored a bluntly-worded statement issued by the New Zealand Embassy in Tokyo last week making it very clear New Zealand did not want ships from the Japanese whaling fleet entering its zone.
McCully's reaction is all about sending signals to the Japanese foreign ministry about the unacceptability of the incursion and the damage that the attitude of the whalers could do to the prolonged diplomatic efforts to find a solution which ends whaling in sub-Antarctic waters once and for all time.
Second, the incursion is not the first time a whaling support vessel has deliberately entered such a zone in order to tail vessels from the Sea Shepherd anti-whaling organisation.
The same ship, the Shonan Maru No 2, entered Australia's exclusive economic zone in February last year, prompting Canberra to lodge an official protest with Tokyo. McCully's response had to be broadly in step with Australia's.
By and large, Japan and New Zealand have been able to quarantine the dispute over whaling from infecting other, more positive aspects of one of New Zealand's longest and strongest international relationships.
McCully's tougher stance reflects frustration with the Japanese and is intended to remind them that the success of that relationship depends on both countries showing mutual respect - something missing given the flouting of New Zealand's wishes with regard to its economic zone.
With Opposition parties breathing down his neck, McCully's stance is also intended for domestic consumption, with National engaged in an election-year shutdown of ticklish issues such as whaling.