The Senate is voting on a 20-week abortion ban. Opponents say it’s “basically relying on junk science.”

On Monday, the Senate will hold a procedural vote on a bill that would make abortion after 20 weeks illegal in every state in the country. Called the Pain-Capable Unborn Child Protection Act, it’s based on the idea that a fetus at 20 weeks’ gestation can feel pain.

“The Pain-Capable Unborn Child Protection Act will protect the voiceless, the vulnerable, and the marginalized,” said Rep. Kevin McCarthy (R-CA), the House majority leader, in a statement in September (the House passed the bill in early October). “It will protect those children who science has proven can feel pain.” While the bill is unlikely to pass the Senate because of the 60 votes required, President Donald Trump has promised to sign the it if it passes; during the campaign, he said such a bill “would end painful late-term abortions nationwide.”

In fact, the best available science shows that fetuses probably cannot feel pain until well after 20 weeks. Advocates of abortion rights say 20-week bans at the state level have harmed women, forcing them to travel to another state, often at great expense, to get the care they seek. And opponents of the Pain-Capable Unborn Child Protection Act fear that, even if it never passes, it will ultimately spread dangerous misinformation.

The bill, sponsored by Sen. Lindsey Graham (R-SC), would ban abortions after 20 weeks nationwide, except in cases of rape, incest, or a threat to the life of the mother. A doctor who performed an abortion after 20 weeks, except in those cases, could face up to five years in prison. Women seeking abortions would not be penalized under the bill.

The text of the bill includes a section on the science of fetal pain, which states that “there is substantial medical evidence that an unborn child is capable of experiencing pain at least by 20 weeks after fertilization, if not earlier.”

However, the general scientific consensus is that no such evidence exists. “There’s actually conclusive evidence that shows that the neurologic structures in a fetus aren’t completely laid down and working yet until much further along in pregnancy, we think even the third trimester,” said Jennifer Conti, a clinical assistant professor and OB-GYN at Stanford University and a fellow with Physicians for Reproductive Health. Twenty weeks, she said, “is just an arbitrary limit set in place by politicians that has no medical or scientific backing.”

The most comprehensive look at fetal pain to date was a literature review published in the Journal of the American Medical Association in 2005. According to the review, the structures needed for fetuses to feel pain begin to develop between 23 and 30 weeks’ gestation, and studies of premature babies suggest they can’t feel pain until 29 or 30 weeks. While this review is now 12 years old, it still holds true — “no research since its publication has contradicted its findings,” wrote Mark S. DeFrancesco on behalf of the American Congress of Obstetricians and Gynecologists in 2015.

The bill makes a number of claims that contradict scientific consensus. For instance, the bill states that “after 20 weeks, the unborn child reacts to stimuli that would be recognized as painful if applied to an adult human, for example, by recoiling.” However, according to the group Advancing New Standards in Reproductive Health (ANSIRH) at the University of California, San Francisco, “limb withdrawal occurs even in full-term babies in response to non-painful tactile sensations, including light touch. Thus the appearance of limb withdrawal on ultrasound represents a reflex rather than a response to pain.”

The bill, said Amy Friedrich-Karnik, senior federal policy adviser at the Center for Reproductive Rights, is “basically relying on junk science.”

The Pain-Capable Unborn Child Protection Act previously passed the House in 2015, as Jessie Hellmann notes at the Hill, but failed in the Senate. Similar bans have also passed in more than a dozen states.

People seek abortions after 20 weeks for a variety of reasons. One patient who came to Conti seeking an abortion said that a clinic the previous week had told her she was 12 weeks pregnant. But the clinic turned out to be a crisis pregnancy center that had given her incorrect information — she was actually 21 weeks along. “Essentially her care was sabotaged,” Conti said — and under a 20-week ban, she would have been unable to get an abortion.

Patients can also be pushed to get abortions later in pregnancy by financial or logistical problems, like difficulty getting to a clinic or getting together the money for the procedure. In states with 20-week bans already in place, patients who need later abortions typically have to travel to another state, said Friedrich-Karnik. That can cause enormous financial strain, she said. But “to imagine a ban like this nationwide and to think that no one could even have the opportunity to go to another state to get the care is frightening.”

The bill passed the House by a vote of 237-189. It probably will not pass the Senate, Hellmann writes, where it would need a 60-vote majority. Republicans may be using Monday’s vote as a way to put pressure on Democratic senators in red states, like Claire McCaskill (D-MO) and Heidi Heitkamp (D-ND), Hellmann noted in January. Both voted against the 20-week ban in 2015, and anti-abortion activists hope a vote against the bill this year will make the senators vulnerable in November’s elections.

Even if it never becomes federal law, Conti said, the bill can still cause harm. “By even putting this issue on a national platform,” she said, “you’re misleading the American people.”

“You’re really providing false and dangerous information that is affecting millions of women,” she added.