Many so-called organic eggs are produced at chicken houses where birds are packed into warehouses and rarely see the sun, a new report from the nonprofit Cornucopia Institute finds.

The group's "Scrambled Eggs" report includes a scorecard with ratings for more than 130 organic egg brands against 28 criteria, including outdoor space, flock sizes, and whether chicks are raised in industrial conditions before arriving at the farm.

The group used a combination of surveys, aerial photography and unannounced site visits to determine the grades.

US regulations for organic egg layers only require "some" outdoor access, which in practice can be met by opening one door in a massive facility with thousands of chickens to a small chicken "porch."

More than two dozen met the highest "5-egg" standard, which means they are small family-run operations that raise hens in mobile housing on well-managed and ample pasture.

But more than 75 of the brands scored the lowest rating, with industrial-scale operations and outstanding concerns about their compliance with US Department of Agriculture regulations. Some had up to 200,000 birds in a single building.

The USDA depends on private companies hired by the farms to certify organic facilities, a practice critics say creates a conflict of interest.

Cornucopia Institute last year filed complaints about large-scale organic egg producers Herbrucks, Krehers, Delta Egg Farm, Chino Valley and Bushman Farms.

The USDA declined to investigate because they were all in good standing with certifying companies.

Read More:

• Organic Egg Scorecard (Cornucopia Institute)
• Millions Of ‘Organic' Eggs Come From Industrial Scale Chicken Operations, Group Says (Washington Post)
• Free-Range Eggs Aren't What You Probably Think They Are (Quartz)