Nixon wouldn't say if he would sign the repeal of voter-approved Proposition B, which otherwise would go into effect in November.
The proposition, which voters approved last November, sets up new standards, including requiring dog breeders to increase dog-space requirements to 12 square feet for small dogs and 30 square feet for large dogs.
Under the current law and in the repeal bill passed by the Legislature, dogs can be housed in stacked cages 6 inches longer and wider than the dog.
"We're prepared to start gathering signatures immediately" to trigger a voter referendum, American Society for the Prevention of Cruelty to Animals legislative initiatives Senior Director Cori Menkin told the St. Louis Post-Dispatch.
Those fighting the bill argue the state Legislature ignored voters, who approved the more stringent requirements.
"That is a travesty of justice, a travesty of our democratic process," Democratic state Rep. Margo McNeil of Florissant told The Kansas City (Mo.) Star.
But those sponsoring the repeal legislation justified changing the voter-approved law because they said voters didn't realize the far-reaching consequences of what they were voting for.
"We have a responsibility to do what's right," Republican state Sen. Mike Parson of Bolivar told the Star. "Whether it's a piece of legislation or an initiative petition, if it's wrong we have an obligation to change it."
Added Republican state Rep. Mike Lair of Chillicothe: "Dogs are property. Dogs don't have rights."