Story highlights The Center for Reproductive Rights says it plans to sue the state

The most restrictive law bans abortions after a fetal heartbeat is detected

Experts say a fetal heartbeat can be detected as early as six weeks

Gov. Jack Dalrymple says it is a legitimate attempt to test the boundaries of Roe v. Wade

What is being called the nation's toughest anti-abortion measure -- a law that bans most abortions after six weeks, when a fetal heartbeat can be first detected -- was signed into law on Tuesday by North Dakota's governor.

The law sets the stage for an almost guaranteed legal showdown, with proponents saying the law is intended to test the 1973 U.S. Supreme Court ruling that made abortion legal.

"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," Gov. Jack Dalrymple said in a statement.

The governor directed the legislature to set aside funds to cover the cost of the expected legal battle, which opponents vowed to mount if the governor signed the measure into law.

"North Dakota's governor today effectively banned abortion in the state, with an outrageous and unconstitutional law that will not stand," said Cecile Richards, president of the Planned Parenthood Action Fund.

Dalrymple called the constitutionality of the law "an open question," saying the Supreme Court has never considered the "precise restriction" of the fetal heartbeat aspect.

The Center for Reproductive Rights announced plans late Tuesday to file a lawsuit to challenge the new law.

"We will not allow this frontal assault on fundamental reproductive rights to go unchallenged," Nancy Northup, the president of the Center for Reproductive Rights said.

While the law does not spell out a specific time frame when a fetal heartbeat can be detected, experts say it is typically six to seven weeks into a pregnancy.

Under the law, a woman who undergoes an abortion in which a fetal heartbeat has been detected may not be prosecuted for violating the law or conspiracy to violate the law.

The law does not rule out abortions when a medical emergency threatens the life of a woman.

It does not allow for an abortion in the case of rape or incest, according to Democratic state Sen. Jim Dotzenrod, who voted against the bill.

Abortion was legalized in all 50 states in 1973 by the U.S. Supreme Court. Statutory time limits on when abortions can take place, however, vary from state to state.

Under Roe v. Wade, abortions are generally permitted until the fetus is considered viable, or able to live outside the womb. Some states have no time limit, while others allow abortion up to the end of the second trimester, about 27 or 28 weeks into the pregnancy.

North Dakota's fetal heartbeat law was one of three laws targeting abortion that Dalrymple signed on Tuesday.

The other laws are:

-- A ban on the procedure on the basis of genetic defects or gender selections.

-- A requirement that doctors who perform abortions have privileges at a North Dakota-area hospital.

While proponents say the law will protect the welfare of a woman undergoing a medical procedure, opponents say it will force the closure of North Dakota's only clinic that performs abortions.

The laws are set to go into effect on August 1, though a legal challenge could postpone them until the matter is sorted out.

The state's Democratic governor, Mike Beebe, vetoed the bill, but the Arkansas House voted to override the veto.

The Center for Reproductive Rights and the ACLU have vowed to challenge the law in federal court.

Called the Arkansas Human Heartbeat Protection Act, the bill requires testing to determine "whether the fetus that the pregnant woman is carrying possesses a detectible heartbeat."