The bill's main sponsor, Rep. Phil Jensen, said the measure merely seeks to make self-defense laws consistent with other South Dakota laws that allow murder or manslaughter charges for the death of an unborn child.
"This has nothing to do with abortion. This is a self-defense bill," Jensen, R-Rapid City, told The Associated Press.
The bill originally sought to allow a pregnant woman to use force to protect her unborn child without being prosecuted for homicide or assault. But in a committee hearing last week, lawmakers broadened the bill to also allow a woman's relatives to claim justifiable homicide if they killed someone to protect the unborn child.
Rep. Peggy Gibson said that could allow someone to claim self-defense for killing abortion providers, including doctors, nurses and other staff at abortion clinics.
"If this bill passes, in theory it would allow a woman's father, mother, son, daughter or husband to kill anyone who tried to provide that woman with an abortion. It's a license to kill abortion providers," said Gibson, D-Huron.
Gibson also feared that the language in the bill would allow extremists to kill abortion doctors and then claim they did so to protect an unborn child.
That was the defense used by anti-abortion activist Scott Roeder, who fatally shot Dr. George Tiller - one of the nation's few late-term abortion providers - inside a Kansas church in May 2009. Roeder, who is serving life in prison, argued during his murder trial that the shooting was justified because he was saving the lives of unborn children.
Jensen said his proposal wouldn't allow such defenses. He said self-defense can be used against illegal attacks, not against legal acts such as abortion.
"This provides a defense not only for (the pregnant woman), but also for someone coming to the aid of her unborn child, the defense of her unborn child," Jensen said.
Jensen said he planned to talk with Attorney General Marty Jackley on Wednesday about the bill's language.
Under the bill, homicide would be justifiable if committed in the lawful defense of an unborn child or to prevent harm likely to result in the death of an unborn child. The bill was expected to be debated in the South Dakota House on Wednesday.
Gibson said she planned to propose an amendment making it clear that the measure couldn't be used as a defense against killing abortion providers.
She also said the bill opens up the possibility that a pregnant woman could kill her boyfriend or husband if they get into a dispute and the man shoves or punchers her.
"It's an open invitation to allow every domestic dispute involving a pregnant woman to escalate into justifiable homicide," Gibson said. "If she feels she's protecting her unborn child, she can shoot him and it's justifiable."
Gibson said the bill would essentially justify murder, adding: "We're taking South Dakota back into the cave age, the Neanderthal age."