He said the rules protected against exploitation of Champagne's reputation, imitation, evocation or any use likely to mislead consumers.
"[We] ask you to immediately amend or delete any reference to 'Champagne' and to refrain from associating your beer with Champagne."
But Moa refused to back down, saying it was being bullied.
Publicist Sunil Unka said: "We thought the letter was a little bit overbearing and petty".
"It's fairly obvious that we're a brewery in the business of brewing beer and unmistakably from New Zealand. We're not trying to pass ourselves off as a sparkling wine from France.
After taking legal advice, the brewery will stand by the descriptions.
Mr Unka said the case was the latest in a spate of large companies bullying smaller businesses.
He cited dairy giant Fonterra's battle to prevent a Waikato cheese-maker from using the word "vintage" to describe its gouda. As well, this week DB Breweries forced a Central Otago brewery to stop calling its beers "Radler", because DB trademarked the name in 2003.
Moa Beer responded to the Champagne letter with a flippant postcard.
One side has a photo of the sinking Rainbow Warrior - bombed by the French Secret Service in 1985 - and a caption with the operation's codename, "Operation Satanique".
The other side reads "Pokokohua Haere Atu - Moa Beer" which, in the company's words, was the closest phrase to "F*** you" in Maori.