Republicans in the Iowa Legislature are backing newly filed legislation that would ban abortions once a foetal heartbeat is detected, which would be the strictest ban in the country if enacted.

A GOP-led House committee had been set to vote on the provision Tuesday night but lawmakers later adjourned without a decision. It's expected to be taken up again Wednesday.

The measure was added to a separate bill that would ban most abortions at 20 weeks of pregnancy. The new version would include several abortion restrictions.

Democrats criticised the legislation in an afternoon press conference, though they don't have the legislative power to stop the bill's advancement.

“This is an all-out assault on women and a sneak attack from Republicans at the last minute,” said Democratic Rep. Beth Wessel-Kroeschell, a ranking member of the House Human Resources Committee that was set to take up the measure.

GOP Rep. Shannon Lundgren, a committee member and the bill's floor manager, said Democrats should not be surprised by the move. She also acknowledged backers of the bill are still securing enough support from other House Republicans.

“Overall, we are a pro-life caucus,” she said. “We've been talking about running a bill through our committee since the beginning of session. Republicans ran on pro-life issues.”

Planned Parenthood of the Heartland spokeswoman Rachel Lopez sent out a press release calling it the “most extreme and overreaching abortion legislation ever introduced in Iowa.”

If the new version of bill is passed, it would still require floor votes in both chambers before it could reach the Republican governor's desk. Ben Hammes, a spokesman for Governor Terry Branstad, did not immediately comment on support for the bill.

“Obviously, Governor Branstad is very pro-life,” Hammes said in an email. “But until we see legislation in its final form, we will reserve judgment.”

Ed Failor, a spokesman for Senate Majority Leader Bill Dix, said in an email, “we do not wish to comment on house actions as they move through their process.”

Among provisions in the amendment:

A pregnant woman will need to wait 72 hours, or three days, before she can get an abortion.

State health officials would be required to make available to a woman seeking an abortion reading material that encourages adoption. It would include language stating Iowa's interest in promoting adoption over abortion.

A woman seeking an abortion would need to sign documentation acknowledging she was told a heartbeat was detected and the statistical probability of bringing the pregnancy to term.

A woman or her spouse could sue a doctor in certain instances for performing an abortion. Parents could sue the physician if the woman was a minor or unmarried.

A legal clause would state that if a part of the bill is found invalid, it does not affect other provisions.

The so-called “heartbeat bill” would prohibit most abortions once a foetal heartbeat is detected, which can be as early as six weeks into pregnancy. Ohio Governor John Kasich vetoed a similar measure late last year. In January 2016, the US Supreme Court refused to review lower court rulings overturning North Dakota's so-called foetal heartbeat law.

A handful of states have introduced heartbeat bills this year, according to the Guttmacher Institute, a research group that supports abortion rights.

Supreme Court strikes down abortion restrictions Show all 23 1 /23 Supreme Court strikes down abortion restrictions Supreme Court strikes down abortion restrictions Abortion rights activists hold placards outside of the US Supreme Court ahead of an expected ruling on abortion clinic restrictions on June 27, 2016 in Washington, DC. Mandel Ngan/AFP/Getty Supreme Court strikes down abortion restrictions An abortion rights activist holds placards outside of the US Supreme Court before the Court struck down a Texas law placing restrictions on abortion clinics on June 27, 2016 in Washington, DC. The US Supreme Court on Monday struck down a Texas law placing a raft of restrictions on abortion clinics, handing a major victory to the "pro-choice" camp in the country's most important ruling on the divisive issue in a generation. Mandel Ngan/AFP/Getty Supreme Court strikes down abortion restrictions WASHINGTON, DC - JUNE 27: Pro-life activists pray on the steps of the United States Supreme Court on June 27, 2016 in Washington, DC. In a 5-3 decision, the U.S. Supreme Court struck down one of the nation's toughest restrictions on abortion, a Texas law that women's groups said would have forced more than three-quarters of the state's clinics to close. Pete Marovich/Getty Supreme Court strikes down abortion restrictions WASHINGTON, DC - JUNE 27: Texas abortion provider Amy Hagstrom-Miller looks on as Nancy Northup, President of The Center for Reproductive Rights speaks to the media outside of the U.S. Supreme Court on June 27, 2016 in Washington, DC. In a 5-3 decision, the U.S. Supreme Court struck down one of the nation's toughest restrictions on abortion, a Texas law that women's groups said would have forced more than three-quarters of the state's clinics to close. Pete Marovich/Getty Supreme Court strikes down abortion restrictions An abortion rights activist holds placards outside of the US Supreme Court before the Court struck down a Texas law placing restrictions on abortion clinics on June 27, 2016 in Washington, DC. The US Supreme Court on Monday struck down a Texas law placing a raft of restrictions on abortion clinics, handing a major victory to the "pro-choice" camp in the country's most important ruling on the divisive issue in a generation. Getty Supreme Court strikes down abortion restrictions Texas abortion provider Amy Hagstrom-Miller wipes a tear as she walks down the steps of the United States Supreme Court with Nancy Northup, President of The Center for Reproductive Rights on June 27, 2016 in Washington, DC. In a 5-3 decision, the U.S. Supreme Court struck down one of the nation's toughest restrictions on abortion, a Texas law that women's groups said would have forced more than three-quarters of the state's clinics to close. Pete Marovich/Getty Supreme Court strikes down abortion restrictions Abortion rights activists cheer after the US Supreme Court struck down a Texas law placing restrictions on abortion clinics, outside of the Supreme Court on June 27, 2016 in Washington, DC. In a case with far-reaching implications for millions of women across the United States, the court ruled 5-3 to strike down measures which activists say have forced more than half of Texas's abortion clinics to close. Mandel Ngan/AFP/Getty Supreme Court strikes down abortion restrictions Abortion rights activists cheer after the US Supreme Court struck down a Texas law placing restrictions on abortion clinics, outside of the Supreme Court on June 27, 2016 in Washington, DC. In a case with far-reaching implications for millions of women across the United States, the court ruled 5-3 to strike down measures which activists say have forced more than half of Texas's abortion clinics to close. Mandel Ngan/AFP/Getty Supreme Court strikes down abortion restrictions WASHINGTON, DC - JUNE 27: Abortion rights activists Morgan Hopkins of Boston, left, and Alison Turkos of New York City, celebrate on the steps of the United States Supreme Court on June 27, 2016 in Washington, DC. In a 5-3 decision, the U.S. Supreme Court struck down one of the nation's toughest restrictions on abortion, a Texas law that women's groups said would have forced more than three-quarters of the state's clinics to close. Pete Marovich/Getty Supreme Court strikes down abortion restrictions Abortion rights activists cheer after the US Supreme Court struck down a Texas law placing restrictions on abortion clinics, outside of the Supreme Court on June 27, 2016 in Washington, DC. In a case with far-reaching implications for millions of women across the United States, the court ruled 5-3 to strike down measures which activists say have forced more than half of Texas's abortion clinics to close. Getty Supreme Court strikes down abortion restrictions WASHINGTON, DC - JUNE 27: Abortion rights activists Morgan Hopkins of Boston, left, and Alison Turkos of New York City, celebrate on the steps of the United States Supreme Court on June 27, 2016 in Washington, DC. In a 5-3 decision, the U.S. Supreme Court struck down one of the nation's toughest restrictions on abortion, a Texas law that women's groups said would have forced more than three-quarters of the state's clinics to close. (Photo by Pete Marovich/Getty Images) Getty Images Supreme Court strikes down abortion restrictions Abortion rights activist Morgan Hopkins of Boston, celebrates on the steps of the United States Supreme Court on June 27, 2016 in Washington, DC. In a 5-3 decision, the U.S. Supreme Court struck down one of the nation's toughest restrictions on abortion, a Texas law that women's groups said would have forced more than three-quarters of the state's clinics to close. Pete Marovich/Getty Supreme Court strikes down abortion restrictions Abortion rights activists embrace after the US Supreme Court struck down a Texas law placing restrictions on abortion clinics, outside of the Supreme Court on June 27, 2016 in Washington, DC. In a case with far-reaching implications for millions of women across the United States, the court ruled 5-3 to strike down measures which activists say have forced more than half of Texas's abortion clinics to close. AFP/Getty Images Supreme Court strikes down abortion restrictions Abortion rights activists hold placards outside of the US Supreme Court ahead of a ruling on abortion clinic restrictions on June 27, 2016 in Washington, DC. In a case with far-reaching implications for millions of women across the United States, the court ruled 5-3 to strike down measures which activists say have forced more than half of Texas's abortion clinics to close. Mandel Ngan/AFP/Getty Supreme Court strikes down abortion restrictions In a case with far-reaching implications for millions of women across the United States, the court ruled 5-3 to strike down measures which activists say have forced more than half of Texas's abortion clinics to close. Mandel Ngan/AFP/Getty Supreme Court strikes down abortion restrictions Abortion rights activists cheer after the US Supreme Court struck down a Texas law placing restrictions on abortion clinics, outside of the Supreme Court on June 27, 2016 in Washington, DC. In a case with far-reaching implications for millions of women across the United States, the court ruled 5-3 to strike down measures which activists say have forced more than half of Texas's abortion clinics to close. AFP/Getty Images Supreme Court strikes down abortion restrictions Abortion rights activists cheer after the US Supreme Court struck down a Texas law placing restrictions on abortion clinics, outside of the Supreme Court on June 27, 2016 in Washington, DC. In a case with far-reaching implications for millions of women across the United States, the court ruled 5-3 to strike down measures which activists say have forced more than half of Texas's abortion clinics to close. / AFP / MANDEL NGAN (Photo credit should read MANDEL NGAN/AFP/Getty Images) AFP/Getty Images Supreme Court strikes down abortion restrictions Abortion rights activists cheer after the US Supreme Court struck down a Texas law placing restrictions on abortion clinics, outside of the Supreme Court on June 27, 2016 in Washington, DC. In a case with far-reaching implications for millions of women across the United States, the court ruled 5-3 to strike down measures which activists say have forced more than half of Texas's abortion clinics to close. / AFP / MANDEL NGAN (Photo credit should read MANDEL NGAN/AFP/Getty Images) AFP/Getty Images Supreme Court strikes down abortion restrictions Abortion rights activists embrace after the US Supreme Court struck down a Texas law placing restrictions on abortion clinics, outside of the Supreme Court on June 27, 2016 in Washington, DC. In a case with far-reaching implications for millions of women across the United States, the court ruled 5-3 to strike down measures which activists say have forced more than half of Texas's abortion clinics to close. AFP/Getty Images Supreme Court strikes down abortion restrictions Pro-choice activist, Alissa Manzoeillo, of Washington, D.C. waits for rulings in front of the U.S. Supreme Court on June 27, 2016 in Washington, DC. A ruling is expected in Whole Woman's Health v. Hellerstedt, a Texas case the places restrictions on abortion clinics, as well as rulings in the former Virginia Governor's corruption case and a gun rights case. Pete Marovich/Getty Supreme Court strikes down abortion restrictions Abortion rights activists cheer after the US Supreme Court struck down a Texas law placing restrictions on abortion clinics, outside of the Supreme Court on June 27, 2016 in Washington, DC. In a case with far-reaching implications for millions of women across the United States, the court ruled 5-3 to strike down measures which activists say have forced more than half of Texas's abortion clinics to close. Supreme Court strikes down abortion restrictions Abortion rights activists hold placards outside of the US Supreme Court ahead of an expected ruling on abortion clinic restrictions on June 27, 2016 in Washington, DC. AFP/Getty Images Supreme Court strikes down abortion restrictions Abortion rights activists hold placards outside of the US Supreme Court ahead of an expected ruling on abortion clinic restrictions on June 27, 2016 in Washington, DC. AFP/Getty Images

If enacted in Iowa, the measure is expected to face legal challenges over its constitutionality. The US Supreme Court's 1973 Roe v. Wade ruling established a nationwide right to abortion, though states were permitted to restrict abortions after viability — the point when the foetus has a reasonable chance of surviving under normal conditions outside the uterus. The ruling offered no legal definition of viability, saying it could range between 24 and 28 weeks into a pregnancy.