Jeremy Birks was "completely shocked" when he saw the horn listed for sale.
"This trade is abhorrent, grotesque and should not be tolerated in New Zealand, of all places," he said.
"Light needs to be shown on this 'secondary' trade in illegal, unethical animal cruelty."
While aristocracies pursued exotic and unusual items from the natural world unabated for centuries, international regulations are now designed to stop the killing of endangered animals.
Global agreements like the Convention on International Trade in Endangered Species (CITES), of which New Zealand is a signatory, regulates and monitors trade in animal and plant species to ensure it does not threaten their long-term survival in the wild.
Mr Grigg said the rhino horn sale meets all rules and regulations.
Any buyer or potential buyer must be aware that it falls under the regulations of CITES and it can't be exported out of the country, or imported into another country, without a CITES permit, Mr Grigg said.
"I hate poaching, it's abhorrent, and everyone here hates it," he said.
"If we had half a sniff that something we had here wasn't that old, I wouldn't be going near it."
Cordy's has sold a pair of African rhinoceros horns, which were inherited items from Dardistown Castle in Ireland, on several occasions in recent years.
The auction house also just sold an 18th/19th century Chinese rhinoceros horn libation cup for $66,000.
In 2013, Webb's auction house in Auckland sold a pair of carved rhino horns for $797,300 in a record-breaking sale.
"Though some people will find all animal-derived antiques distasteful or immoral, an interest in objects of ivory and horn often does co-exist with a desire to protect and preserve the natural world," Mr Grigg said.
"Not selling an old rhino horn, however, does not stop poachers in Africa."
Criticism of the sale also raises the issue of whether auction houses or traders should be allowed to sell fur coats, Nazi memorabilia, ivory items, or whalebone carvings, Mr Grigg said.
Hans Kriek, executive director of animal rights organisation SAFE, is against the sale.
"It feeds into the idea that it's somehow desirable to have a dead, endangered animal on your mantelpiece -- it's a weird thing to do, I don't know why people like to have dead animals as trophies," he said.
"And while the damage has been done a long time ago, what would stop someone from buying it and selling it in Asia, for example, where these horns are very valuable."
Rhino poaching is at a crisis point, according to conservation group Save the Rhino.
It says that at least 1338 rhinos were killed by poachers across Africa in 2015.
Rhinoceros horn is worth more than its weight in gold or platinum, according to the International Rhino Foundation, with its major markets of China, Japan and Vietnam prizing it for its so-called medicinal properties.
