The Equine Welfare Alliance blamed animal agriculture associations for the current push across states in the farming belt to show support for the return of horse abattoirs.
"While most of the bills are little more than non-binding resolutions, a few are truly draconian," said alliance representatives John Holland and Vicki Tobin in a statement.
"The Montana bill (HB 418) would prohibit courts from issuing injunctions against horse slaughter facilities and require expensive bonds and impose penalties on anyone attempting a legal challenge to building a horse slaughter house," they said.
"Passage of such a bill would be an insult to the memory of the brave men and women who more than 200 years ago fought for every man's unfettered access to the courts."
On Thursday the bill moved to the Senate Agriculture committee for hearings, after it was passed by Montana's House of Representatives.
"But even as the Montana Senate Agriculture committee listened to the debate, the North Dakota Senate decided similar language in their pro-slaughter bill (HB 1496) was too much and they stripped it out.
"The language, known as Section I, would have required anyone contesting the construction of a horse slaughter plant to post a bond equal to 20% of the construction cost. As it now stands, their bill provides for $50,000 to fund a study on the feasibility of building a horse slaughter plant.
"While clearly targeted at horse advocates and animal rights activists, the Montana bill would prevent all citizens from challenging the building of a plant in their neighborhoods."
The pair dismissed suggestions the anti-slaughter lobby had a secret agenda of wanting to ban all meat.
"The argument, if it wasn't so pitiful, would be laughable," Holland and Tobin said. "Can any American really believe for a moment that we can give up our love of one of the nation's great institutions, the hamburger? We counter that there will likely always be a McDonald's."
Among opponents to the bill was Paula Bacon, the former mayor of Kaufman, Texas, who told of her prolonged fight to rid her town of the Dallas Crown slaughter plant.
"Bacon provided the committee with documentation of the years of pollution and other problems her town suffered from blood backing up into bathtubs to a nearby hospital that was forced to install air filtration because of stifling odors. Other opponents to the bill objected strictly on the basis that it deprived the citizens of their legal rights."