"The shallow thinking exposed by this argument totally ignores the millions of beef, pork and chicken eaters who are revolted by the prospect of killing a non-food animal such as a horse or dog for profit," said alliance representatives John Holland and Vicki Tobin.
Slaughter advocates have "thrown their misinformation campaign into high gear", they claim.
"Their arguments, when exposed to critical examination, fall apart like the succulent beef of a well cooked roast. They have escalated efforts to scare the livestock industry into believing that ending horse slaughter is the first step to banning the slaughter of livestock."
The alliance says the Federal Prevention of Equine Cruelty Act of 2009 could not be more clear in its intent: an end to horse slaughter.
"It is not, as recently asserted, an act to criminalise horse meat," Holland and Tobin said in a statement.
"More importantly, the legislation is absolutely, unequivocally, indisputably, not the beginning of a vegetarian-led effort to end animal agriculture in this country. Such claims are, in the jargon of animal agriculture, just plain hogwash."
Supporters of ending slaughter are being portrayed as tree-hugging vegans and animal welfare crazies, the pair say.
They singled out Wyoming State Representative Sue Wallis, saying her recent paper on the horse slaughter issue indicated that she "missed her calling as a fiction writer".
"The entire premise of Representative Wallis' dissertation on horses as a food source is negated by the fact that horses are not classified as food animals by the United States Department of Agriculture and are, in fact, classified by the Food and Drug Administration as companion animals.
"She argues that owners have the right to dispose of their 'property' in any manner they choose, oblivious to disposal laws on appliances, cars, computer equipment, toxic waste materials and, in some areas, horses. Wallis cannot change history any more than she can change the grim reality of horse slaughter," Holland and Tobin said.
"In survey after survey, more than 70 per cent of the American public has gone on record saying they don't want horse slaughter.
"Congressman Conyers and Senator Landrieu, who introduced the federal legislation, are respected legislators that have been elected to multiple terms. Neither could be remotely considered tree-hugging vegans out to ban livestock slaughter.
"Conyers comes from a state where midwestern beef is revered. Landrieu hails from Louisiana, and anybody knows that if something moves in that state it will likely end up in a pot to make a spicy Creole dish. Radical vegans? Hardly!
"With rare exception, equine welfare advocates are meat eaters. Ending horse slaughter is not going to take away our hamburgers, sausage, chops and steaks."