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(CNN) —  

Iowa Gov. Kim Reynolds signed legislation on Friday that prohibits doctors from performing an abortion if a fetal heartbeat is detected.

The legislation, which has been called “the heartbeat bill,” is widely described as the nation’s most restrictive abortion ban.

Reynolds, a Republican, acknowledged that the law is expected to face legal challenges on Friday as she explained her support for the law as rooted in religious conviction.

“I understand and anticipate that this will likely be challenged in court,” the governor said in a statement. “However, this is bigger than just a law. This is about life.”

She added, “it is immoral to stop an innocent beating heart … my faith leads me to protect every Iowan, no matter how small.”

Shortly after the bill signing, the American Civil Liberties Union announced plans to sue to stop the law from going into effect.

Iowa’s Republican-controlled legislature passed the legislation earlier this week. The legislation, Senate File 359, states that except in medical emergencies, doctors are not allowed to perform an abortion before testing for a fetal heartbeat. It requires a physician to notify the woman seeking an abortion in writing whether a heartbeat is detected and that abortion is barred in the event that it is detected. Fetal heartbeats can be detected as early as six weeks into a pregnancy.

Critics have pointed out that the legislation would effectively ban abortion at six weeks and before a woman is aware that she is pregnant.

NARAL Pro-Choice America president Ilyse Hogue responded to the bill signing on Friday, saying it was “a sad day for women and families in Iowa” and that the law bans abortion “before most women even know they’re pregnant.”

Political opponents have already seized on the bill to attack Reynolds.

Fred Hubbell, a candidate for the Democratic nomination in the upcoming governor’s race, said in a statement that Reynolds “has once again proven that she is willing to put political extremism over the health, well-being and rights of Iowa women.”

Meanwhile, organizations that oppose abortion rights cheered the governor’s decision.

“The bold pro-life action taken by the Iowa legislature reflects growing national pro-life sentiment and restlessness under the extreme status quo imposed by Roe v. Wade,” Marjorie Dannenfelser, the president of pro-life group Susan B. Anthony List said in a statement. “While Roe has not yet been reversed, it has been soundly rejected in the court of public opinion.”

Some Iowa Republican lawmakers hope that the legislation is eventually taken up by the Supreme Court as part of an effort to challenge Roe v. Wade, the landmark Supreme Court decision legalizing abortion nationwide.

“This bill will be the vehicle that will ultimately provide change and provide the opportunity to overturn Roe v. Wade,” Iowa Republican state senator Rick Bertrand said of the legislation during floor debate. “There’s nothing hidden here about the agenda. You know, today the pro-life movement won a battle, but the war rages on.”

CNN’s Saeed Ahmed, Isabella Gomez and Marlena Baldacci contributed to this report.