(CNN) The Republican-led legislature in Iowa has passed a bill that, if signed into law, will become the nation's most restrictive abortion ban: It forbids doctors from performing the procedure after a fetal heartbeat is detected.

In many cases, that can happen as early as six weeks into a pregnancy, before many women even know they're expecting.

Right now, Iowa bars most abortions after 20 weeks, already making it one the most restrictive states. But Senate File 359 , or the "heartbeat bill," ups the ante.

And it's most certainly going to be challenged in court, opponents say.

In 2013, North Dakota passed a similar law that banned abortions after six weeks . The case made its way to the US Supreme Court, where it was blocked permanently.

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