A new report from the Wisconsin-based Cornucopia Institute says some producers of organic milk aren't following federal standards.
Wisconsin ranks number one in the country for the most "certified organic" milk cows.
Most of the more than 70,000 cows produce milk on small family farms with plenty of room for cows to move around.
Pasture access is one of the requirements for getting organic certification.
But Cornucopia spokesman Mark Kastell says ten mega-dairies in western states are skirting the rules by denying the cows access to pastures.
Kastell also says the USDA isn't strictly enforcing the rules.
Cornucopia's study has a scorecard for 68 organic dairies, ranking them by how closely they follow federal standards.
The National Organic Standards Board is expected to discuss changes in pasture access rules next month.