Moa beer chief Geoff Ross has accused big brewers Lion and DB of not playing fair and moving aggressively to block independent beer companies from pubs and supermarket shelves.
Ross said the rise of craft beer had prompted a shift in attitude from the big foreign players.
Lion is owned by Japanese brewer Kirin and DB by Europe's Heineken.
Independent breweries accounted for 10 per cent of total beer consumption by value last year, according to the ANZ Craft Beer Industry Insights report. That's up from 8.5 per cent in 2015.
"It was always the case that there were Lion pubs where you wouldn't find DB and DB pubs where you wouldn't find Lion," said Ross.
"When craft beer came into being, bar owners would put a few craft brands into the chiller. Lion and DB turned a blind eye. But now that craft beer is a growth segment and a meaningful part of the beer landscape, that's when they've bought in blocking tactics, where they've actively blocked any brand that becomes a threat."
As Moa had grown and become more of a threat to DB and Lion, it was now being specifically excluded, he claimed.
But Lion denies that is the case.
"From a Lion perspective that is completely wrong. Moa is not mentioned in Lion contracts. Publicans have their own reasons for choosing not to stock Moa's portfolio," said Lion external relations manager Genevieve O'Halloran.
She also rejected any suggestion that Lion was adopting more aggressive tactics.
"Absolutely not," she said. "In fact we are seeing small craft beers contracting taps in some outlets, and good on them."
DB was also approached for comment.
"The specific terms of DB's agreements with its customers are commercially sensitive," said Paul Millward, DB Breweries sales director. "DB continues to focus on providing its customers with a great range of consumer-inspired, relevant products and tailored support options."
Ross said he wanted to emphasise that Moa was open to more competition, including from international players, but he felt the dominance of DB and Lion represented a duopoly which was limiting consumer choice.
"We should absolutely welcome offshore beer brands into New Zealand. As they should us into their countries, which they do," he said.
But Moa claimed it was now facing more barriers to competition in New Zealand than in its offshore markets.
As more craft beer brands started to operate in the grocery space, that had also prompted more restrictive practices from the big players, he said.
"I guess that's a benefit of size, which you find in a lot of marketplaces. They [Lion and DB] have scale and they leverage that."
But he claims that marketing representatives for Lion and DB have been undermining Moa's position on supermarket shelves by "pulling Moa and other brands off the shelf, shifting them to a less prominent position, and even removing price tags.
"We've seen it. And in a few instances we've caught them red handed. So that's going on," he said.
Both Lion and DB said they were not aware of this occurring, and Moa had not raised the issue with them.
Tim Carroll, Countdown merchandise manager, alcohol, said Moa had not raised any of these concerns with him, but he would get in touch with Ross to discuss the issue.
However, he rejected suggestions that getting shelf space was tougher for small brewers.
"Over the past two years, Countdown's range of craft beers has doubled, as has the shelf space dedicated to craft beers in Countdown stores," Carroll said.
Given the limited space, that growth had come at the expense of the mainstream brands.
He also emphasised that shelf space was determined on the merits and popularity of each product.
"We have no financial agreement with any brewer to sell shelf space."
Foodstuffs echoed those views.
Claims of product tampering were "ridiculous", said Foodstuffs media spokesperson Antoinette Laird. "This activity would not be tolerated by stores and we are confident it is not happening."
Commercial agreements were confidential, but to say they related to shelf space was inaccurate, she said.
"We stock the products our customers desire. And the burgeoning craft beer demand from our customers is a great example of this."
Lion's O'Halloran said there was huge opportunity for craft brewers.
"There are two new breweries opening in New Zealand every month," she said. "So we refute the assertion that the New Zealand market is too tough for craft brewers."
Moa is listed on the NZX. Its shares closed down 1c yesterday at 46c.