Kris Kitko, left, leads chants of protest at an abortion-rights rally at the state Capitol in Bismarck, N.D. March 25, 2013. (James MacPherson/AP)

A federal judge in North Dakota on Monday temporarily blocked the state’s law banning abortions as early as six weeks after fertilization, calling the legislation “clearly unconstitutional.”

The preliminary injunction from U.S. District Judge Daniel L. Hovland means that the nation’s most restrictive abortion law, which would bar abortions as soon as a fetal heartbeat is detectable, will not take effect Aug. 1 as planned.

The ruling also suggests that, even as states across the country enact measures limiting abortion access, some of the laws may never take effect because of stiff legal challenges.

Hovland’s ruling criticized the North Dakota measure in harsh terms, calling it “clearly unconstitutional under an unbroken stream of United States Supreme Court authority.”

“The State has extended an invitation to an expensive court battle over a law restricting abortions that is a blatant violation of the constitutional guarantees afforded to all women,” Hovland wrote. “The United States Supreme Court has unequivocally said that no state may deprive a woman of the choice to terminate her pregnancy at a point prior to viability.”

While the issue of viability is left to individual doctors to determine, it is usually considered to be 24 weeks after fertilization.

Jeff Zent, a spokesman for North Dakota Gov. Jack Dalrymple (R), declined to comment on the ruling. “It’s standard practice in our office not to comment on ongoing litigation,” he said.

When Dalrymple signed the bill into law in March, he acknowledged that it would face a major fight in court. Several other new abortion laws, in states ranging from Wisconsin to Arizona, are being challenged in state and federal courts.

“Although the likelihood of this measure surviving a court challenge remains in question, this bill is nevertheless a legitimate attempt by a state legislature to discover the boundaries of Roe v. Wade,” Dalrymple said in a statement at the time.

The injunction by Hovland was issued in response to a request from the Center for Reproductive Rights. Bebe Anderson, director of the group’s U.S. legal program, praised the ruling.

“The nation’s most extreme abortion ban has been blocked, and the message to hostile politicians could not be clearer: The rights of women guaranteed under the U.S. Constitution and protected by 40 years of Supreme Court precedent cannot be legislated away,” Anderson said.