Wal-Mart Stores Inc. is the target of an unlikely alliance between a labor union and farmers and ranchers who say the world’s largest retailer is using its power to hold down prices in the agriculture industry.

The United Food and Commercial Workers International Union, which has tried unsuccessfully to unionize Wal-Mart’s employees, is urging the Obama administration to broaden its antitrust inquiry into meat, dairy and seed businesses to include the retailer. Wal-Mart’s defenders say its policies benefit consumers, ensuring them low prices.

The viewpoint of the union, the UFCW, is echoed by such groups as the National Farmers Union, a 190,000-member organization. Until recently, farmers and ranchers had mostly been directing their ire at meat producers such as Tyson Foods Inc. and Smithfield Foods Inc. Now some are saying Wal-Mart, whose motto is “Save money. Live better,” is unfairly cutting food costs at their expense.

“We’ve got to really join forces if we’re going to win against this abusive market power,” Mike Callicrate, a rancher based in Colorado Springs, Colorado, said in an interview.

Wal-Mart’s critics said they anticipate, after years of government reluctance to regulate farming, that President Barack Obama will inject more competition into the food-producing business. Those concerns were at the forefront of an Aug. 27 public meeting in Fort Collins, Colorado, with Attorney General Eric Holder and Agriculture Secretary Tom Vilsack.