Whole Foods' proposed buyout of Wild Oats should be blocked because it will lead to higher prices, according to consumer groups.

The Consumer Federation of America, the American Antitrust Institute and the Organization for Competitive Markets filed the brief in Washington federal court, although it wasn't made available to the public until Friday.

A federal judge is considering whether to let Whole Foods proceed with its proposed $671 million purchase of Boulder-based Wild Oats.

The consumer groups endorsed the FTC's argument that Whole Foods competes in a much smaller upscale market for premium produce.

Whole Foods has argued that it and Wild Oats are just a fraction of the larger supermarket industry since Safeway and Kroger have bulked up their organic food offerings.

"We believe this merger will lead to higher prices, less service and diminished consumer choice," the consumer groups said in the brief.