Wisconsin Governor and GOP presidential hopeful Scott Walker on Monday signed a controversial bill into law that bans an abortion after 20 weeks of pregnancy unless the mother’s life is in danger. The law, which was passed by the Republican-controlled state legislature earlier this month, does not provide any exceptions for pregnancies resulting from rape or incest.

Walker, who announced his candidacy for the Republican nomination last Monday, said that the law was necessary to protect the fetus from pain. “At five months, that's the time when that unborn child can feel pain,” Walker reportedly said. “When an unborn child can feel pain, we should be protecting that child.”

Although supporters of the legislation argue that a fetus beyond the 20-week stage can feel pain, and over a dozen U.S. states currently have similar laws, the dominant view within the medical community is that such an assertion is, at best, unproven.

“A rigorous 2005 scientific review of evidence published in the Journal of the American Medical Association (JAMA) concluded that fetal perception of pain is unlikely before the third trimester [25 weeks from fertilization],” the American Congress of Obstetricians and Gynecologists said, in a statement released in 2013. “Although ultrasound monitoring can show intrauterine fetal movement, no studies since 2005 demonstrate fetal recognition of pain.”

During his 2014 gubernatorial reelection campaign, Walker said that he was in favor of a law that “leaves the final decision to a woman and her doctor.” However, the statement was reportedly met with opposition from many anti-abortion activists who questioned his pro-life credentials.

Currently, 43 percent of Americans believe that abortion should be illegal in all or most cases, according to a 2013 Pew survey. In Wisconsin, this number stands at 41 percent.

The provisions of the new law were criticized by many doctors in the state, who said that it tied “the hands of doctors seeking to help women.”

“This is bad medicine, based on the thoroughly debunked fallacy that a 20-week fetus – which is not viable -- can feel pain,” a group of 100 gynecologists wrote in a letter to Walker earlier this month. “Only a woman and her trusted doctors -- not elected officials -- should make decisions about her health.”

Former secretary of state Hillary Clinton -- the clear frontrunner for the Democratic Party's presidential candidate -- also slammed Walker’s decision to sign the “extreme and unacceptable” bill into law.