Illinois is home to the last operating slaughter plant in the US, the meat being exported for human consumption.
The plant was forced to shut recently over a federal court ruling over the supply of meat inspection services by the US Department of Agriculture. However, it later received court approval to resume operations pending the outcome of an appeal.
Texas has two plants, but these have been closed since a court ruling found that 1949 Texas law banned the slaughter of horses for human consumption.
In Illinois, the House last month passed a bill banning the slaughter of horses for human consumption. It has already had the backing of a Senate committee and is now headed for consideration by the state Senate. If passed, it only needs the state Governor to sign off for it to become law.
In Texas, however, the state Senate has just approved an amendment which animal rights campaigners claim is an attempt to overturn the 1949 law that makes the slaughter illegal.
The Society for Animal Protective Legislation (SAPL) said the Senate approved it without any debate.
Animal protection groups called on the House to reject this legislation and to maintain the ban on horse slaughter for human consumption.
"Texas citizens overwhelmingly oppose horse slaughter," said Humane Society of the United States (HSUS) President and CEO Wayne Pacelle. "A 2003 Texas voter poll showed that 72 percent of Texans oppose horse slaughter for human consumption, and 77 percent would vote against any member of the legislature who supported a repeal of the existing horse slaughter ban."
SAPL argues that horse slaughter plants are a drain on the local economy. The two Texas plants are foreign-owned and employ fewer than 130 low-paid, mostly migrant workers. It argues they pay little tax and the profits go overseas.
"Texas has a good strong law against slaughter that reflects the attitudes of the people of the state," said Ed Sayres, president and chief executive of the American Society for the Prevention of Cruelty to Animals. "We must not let a measure that did not even go up for debate overturn what the people find inhumane and unacceptable."
"We hope that Texas legislators oppose this amendment or any other attempt to legalize horse slaughter in the State of Texas," said Chris Heyde, deputy legislative director of the Society for Animal Protective Legislation (SAPL).
"Protecting our horses from slaughter is a priority for Texans and all Americans."