Republican Gov. John Kasich signed a bill Tuesday banning abortions after 20 weeks while vetoing stricter provisions in a separate measure that would have barred the procedure at the first detectable fetal heartbeat.

Kasich acted on both proposals the same day they landed on this desk.

The so-called heartbeat bill would have prohibited most abortions once a fetal heartbeat is detected, which can be as early as six weeks into pregnancy — or before many women even know they're pregnant. Its provisions cleared the Republican-led Legislature during a lame-duck flurry last week after being tucked into separate legislation.

Similar measures elsewhere have faced legal challenges, and detractors in Ohio feared that such legislation would lead to a costly fight in the courts. Opponents predicted that it would be found unconstitutional, a concern Kasich shared.

Ohio lawmakers still have the option to override his veto. Doing so would require a three-fifths majority of each chamber.

Ohio Gov. John Kasich, pictured in September, indicated he believed the abortion 'heartbeat' bill was unconstitutional. Carolyn Kaster / AP

Kasich, an abortion-rights opponent, chose instead to sign off on a 20-week ban similar to those now in effect in 15 states and blocked from enforcement in two others. The measures are based on the assertion that fetuses can feel pain then.

Opponents have challenged the "pain-capable" characterization as scientifically unsound. Ohio lawmakers rejected a Democratic amendment that would have added exceptions for rape and incest.

Republican lawmakers in numerous states — including Texas, Missouri, Iowa, Indiana and Kentucky — plan to push for new anti-abortion legislation. Their efforts are being supported by a national anti-abortion group, Americans United for Life, which released a report Tuesday contending that many abortion clinics are in violation of state health and safety standards.

Related: Is Ohio 'Heartbeat' Bill a Feint Before More Successful Blow to Women's Rights?

In Congress, Republicans are expected to advance legislation banning most abortions after 20 weeks and halting federal funding for Planned Parenthood as long as it performs abortions. President-elect Donald Trump has pledged to support both measures.