Countdown supermarkets, and Foodstuffs, which owns Pak 'n Save and New World, and have said the transition to sell only barn or free range eggs in the next 10 years was driven by consumer pressure, according to Stuff.co.nz.

But according to figures from market research company IRI Aztec, more than 70 per cent of the eggs sold at supermarkets were from standard cages in the three months to September 3. Free range and barn made up a combined 25 per cent.

Safe advertisements have been putting years of pressure on supermarkets to stop selling eggs from caged chickens.

Egg Producers Federation executive director Michael Brooks said cage eggs were more popular than cage free and the transition to cage free would put unrealistic pressure on egg farmers.

Supermarkets made up about 55 per cent of the egg market for farmers, and due to biosecurity restrictions New Zealand can only sell eggs from local farmers.

Sals of a standard box of a dozen cage eggs were up by 550,515 last year, compared to only 60,644 for free range and 82,861 for barn laid.

Foodstuffs would not provide figures on the sales of different eggs by farming system.

In March, Countdown said that 70 per cent of Kiwi shoppers bought cage eggs, while only 30 per cent of the egg sales were from free-range or barn chickens.

But Countdown general manager James Walker said on Monday that stores had seen double digit sales growth for barn and free range.

Some egg farmers have already poured millions of dollars into colony cages after the Ministry for Primary Industries changed the Layer Hens Code of Welfare in 2012.

Farmers were given six years to switch from battery to colony cages, which have more space and perching, nesting and scratching areas.

"Now the supermarkets are saying sorry I know you've spent millions of dollars but in 10 years time we're not taking your eggs and for the farmers it's a really unfair position," Mr Brooks said.

A third generation North Island farmer, who did not want to be named, said he had been working on a plan to switch to a colony system that had already taken two years of transition work and would take another year to finish.

"This now requires a seven figure deposit with full payment a couple of months later in excess of half a million dollars," he said.

Mr Brooks said changing a cage farm to free range or barn meant installing a mechanised egg collection belt to take eggs away from the nestings, and having a big enough shed for 3000 to 5000 hens. Which often meant farmers had to look for a new location.

A Christchurch farmer recently sold his old farm and purchased a new site to comply with the new code, but was challenged by local residents under the Resource Consents Act and had to sell the land and purchase another site 50 kilometres away.

Competition would drive down the price of eggs and make it unviable for egg farmers to continue, Mr Brooks said.

"Costs to produce barn and free range eggs are higher. There is a point beyond which you can't drive down the fixed cost, there's higher mortality and diseases, there's less production, there's cost of land.

"Financial pressure of farmers is often what leads to people making poor decisions, which includes poor welfare."