A federal judge on Friday temporarily blocked enforcement of one of the country’s most stringent abortion laws, an Arkansas ban on the procedure at the 12th week of pregnancy, saying the law was likely to be declared unconstitutional.

Adopted in March, the law was the sharpest challenge yet to the standard set by the Supreme Court. Roe v. Wade in 1973 and later decisions determined that a woman has a right to an abortion up to the point that a fetus is viable outside the womb, usually around 24 weeks.

Abortion rights groups quickly brought a legal challenge, resulting in Friday’s preliminary injunction, which was issued by Judge Susan Webber Wright of Federal District Court in Little Rock. The injunction will prevent the law from taking effect on its scheduled date of Aug. 16 and will remain in place until the judge hears final arguments and rules on its constitutionality.

Also in March, North Dakota passed an even more restrictive law, banning abortions at the sixth week of pregnancy, which is before many women even know they are pregnant. The Center for Reproductive Rights, a New York-based group that challenged the Arkansas law, along with the American Civil Liberties Union, said it planned to file a plea in North Dakota to block that law before it takes effect on Aug. 1.