CHICAGO (Reuters) - The U.S. government is set to shake up the $500 million organic egg industry with rules that for the first time will mandate specific space requirements for hens and spell out what it means for them to have access to the outdoors.

Proposed requirements from the U.S. Department of Agriculture, released on Thursday, aim to increase confidence among consumers about what it means when food products carry an organic label.

Divergent farming practices within the fast-growing organic sector have caused confusion among shoppers and given an economic advantage to egg producers who do not provide as much space for their poultry, according to the USDA.

Some animal advocates said the proposed changes also were a step toward improving animal welfare.

“For all these years, since we’ve had an organics program, it’s been very unclear about the specifics of how animals should be treated,” said Dena Jones, farm animal program director for the Animal Welfare Institute, an advocacy group.

Under the USDA’s proposal, farmers must provide each hen with at least 2 square feet of outdoor space. It defines outdoors as an area in the open air with at least 50 percent soil. The area must have no solid walls or a solid roof attached to the birds’ indoor living space.

The USDA will have a 60-day comment period of the proposal and review the responses. If approved, the rules will be phased in over five years for farms that are already certified as organic.

The new rules would increase the cost of producing one dozen organic eggs by 3.6 percent, the USDA said. The nation produced about 166 million dozen organic eggs in 2014, according to the agency.

Only about 36 percent of organic egg operations provide at least 2 square feet per bird of outdoor space, according to a survey cited by the USDA.

And at least 50 percent of organic egg production comes from operations that exclusively use roofed enclosures, known as porches, to provide outdoor access to hens, according to the agency’s Agricultural Marketing Service. The porches have solid floors and no access to soil. Fresh air enters the porches through screens or netting.

Consumers already believe that organic livestock spend a significant part of their lives outdoors, said Miles McEvoy, deputy administrator of the USDA’s organic program.

The proposed rules “will maintain that consumer confidence in the organic label by maintaining those specific requirements,” he said.

Still, some activists said the USDA should go farther in requiring more space for birds and ensure vegetation is available in their outdoor areas.

The egg industry has undergone a major shift toward cage-free production.