FAIRFIELD, Iowa — Small family-operated dairy farms with cows freely grazing on verdant pastures are going out of business as large confined operations with thousands of animals grouped in assembly-line fashion are expanding into the organic market.

Many traditional small-scale organic farmers are determined to fight back against the industry transformation by urging consumers to look closely at the organic milk they buy to ensure it comes from a farm that meets the idyllic expectations portrayed on the cartons.

While the large operations say they’re meeting U.S. Department of Agriculture standards for organic milk, the smaller farms say federal regulators under Republican and Democratic administrations have relaxed enforcement of strict organic standards for dairy farms, allowing confinement dairies to grow and compete intensely with small family-operated dairies.

“There’s a higher authority than the USDA. There’s a higher authority than the federal courts where we’ve litigated some of these issues. And that’s the consumer. Their dollar has power,” said Mark Kastel at the Wisconsin-based Cornucopia Institute, a nonprofit farm policy-public interest group.

The dairy industry, like much of U.S. farming, has trended toward fewer but larger farms since the 1980s, when organic milk was available only at farmers markets or specialty grocers and the milk came from small-scale dairy farms selling to a local cooperative. Now organic dairy products are widely distributed by mainstream grocers and mass retailers such as Costco, Target and Walmart. But much of those companies’ store-brand milk comes from dairies with thousands of cows maintained in immense confinement operations.

Kastel says that style of farming is contrary to what the founders of the organic movement envisioned and what consumers believe they’re buying. On Thursday his group is releasing an updated Organic Dairy Scorecard , which will rank 160 brands evaluated for their organic practices, including quality of pasture, how frequently cows graze and how often they’re milked.

A spokeswoman for Aurora Organic Dairy, the industry’s largest supplier to grocery chains, said activists who believe organic food should come only from small producers are the primary critics inaccurately portraying large-scale organic production.

Sonja Tuitele said the company’s farms have more than 10,000 acres of organic pasture for grazing, and that the farms exceed minimum requirements for grazing days and percent of diet from grazing.

The company has nine barns in Colorado and Texas with about 26,000 cows. The largest has 4,400 cows and the smallest has 900. Aurora CEO Scott McGinty said in a statement released in April that the company maintains two USDA-accredited certifiers for each farm. Competition from large operations, combined with plummeting dairy prices in the past four years, have left organic dairy farmers either barely squeezing out a profit or in most cases losing money. It has accelerated the loss of smaller farms.

The USDA reported in February that the number of U.S. dairy farms, including organic and conventional, fell nearly 4 percent last year from the previous year to 40,219. In the past decade, the number of dairy farms has declined 32 percent.

For Patti and Brian Wilson, the changing industry has soured the profitability of their 600-acre dream dairy farm in Orwell, Vermont, which they converted to organic 16 years ago. Milking their 50 cows has become unprofitable, said Patti, who was an agronomist with the USDA before she began farming full time.

“We just put an ad out listing our herd for sale,” she said. “It’s been a slow decline, kind of a slow death.”

The strategy adopted by Francis Thicke, a southern Iowa organic dairy farmer, is to work with other farmers to create the Organic Farmers Association, a grassroots group focused on organic policy issues. They have launched the Real Organic Project, an effort to create an additional label that would be placed on packaging to tell consumers that the products meet traditional organic standards. A pilot project this year will have 50 farms with products carrying the Real Organics label.