The veto from Gov. Laura Kelly, a Democrat, sets up a showdown with a Republican-dominated legislature that appears to have the two-thirds majorities needed in both chambers to override the veto. Legislators are scheduled to return from a weeks-long break May 1.
The bill would require abortion clinics to display a sign notifying women that they could stop a medication abortion by taking the hormone progesterone -- even if they have already taken Mifepristone, the first of two drugs used in the procedure -- and doctors would have to tell a patient in writing that a medication abortion could be reversed. A clinic that failed to post a sign could be fined $10,000, and a doctor who failed to notify a patient could be charged with a misdemeanor for a first offense and a felony for a second.
Medication abortions using Mifepristone, also known as RU-486, are the most common way of terminating a pregnancy in Kansas, accounting for 61 percent of the total last year, according to statistics from the state health department.
Supporters of so-called "reversal" laws have cited a 2018 study led by Dr. George Delgado, a board member of the American Association of Pro-Life OB/GYNs and a voluntary associate clinical professor at the University of California, San Diego's medical school. They also noted that progesterone has been used for decades to prevent miscarriages.
Abortion-rights supporters have said the study was flawed and progesterone's use for reversing a medical abortion hasn't been tested adequately. The American College of Obstetricians and Gynecologists has disputed the usefulness of the procedure, stating in August 2017 that "[c]laims regarding abortion 'reversal' treatment are not based on science and do not meet clinical standards."
Seven states with Republican governors have enacted such laws, starting with Arkansas in 2015, and Oklahoma's GOP-controlled legislature recently approved a measure. Kelly was elected last year and took office in January after the state imposed a raft of new abortion restrictions under her Republican predecessors Sam Brownback and Jeff Colyer.
Other states, including Kentucky, Mississippi and Ohio, have moved to ban abortions when a fetal heartbeat is detected, as early as the sixth week of pregnancy. Kansans for Life, the state's most influential pro-life group, has long favored an incremental approach and restrictions that would survive court challenges.
The Associated Press contributed to this report.