The state-by-state assault on women’s rights and the Constitution by Republicans faced an important challenge on Wednesday in Phoenix, where plaintiffs in a federal lawsuit are trying to block an extreme Arizona anti-abortion law from taking effect next week.

The law, signed by Gov. Jan Brewer in April, pushes Arizona to the forefront of a group of states that have recently moved to impose new restrictions on legal abortions, based on medically dubious ideas about when a fetus can begin to feel pain. Arizona has set the earliest deadline in the country. While other states have forbidden abortions more than 20 weeks after fertilization, Arizona bases its time limit on a woman’s last menstrual period, outlawing abortions after about 18 weeks from fertilization. Doctors convicted under the law would face up to six months in prison and could lose their licenses.

Janet Crepps, a lawyer from the Center for Reproductive Rights, which brought the case with the American Civil Liberties Union and three Arizona doctors, took less than an hour to make an elemental argument before Judge James Teilborg of the United States District Court in Phoenix.

The gist of the argument was that the Supreme Court, in Roe v. Wade, has forbidden states to ban abortions before viability: the point at which a fetus can survive outside the womb. That is usually about 24 weeks, but it is determined in individual cases by a doctor. States may try, within limits, to discourage women from having abortions before then, but they may not deprive a woman of her fundamental right to choose an abortion before viability.