On Thursday, the Oklahoma Legislature gave final approval to a bill that would outlaw nearly all abortions beginning with fertilization, making it the nation’s strictest abortion law.

Individuals may sue abortion providers and anyone who “aides or abets” an abortion under the bill. It would go into effect immediately if signed by Republican Gov. Kevin Stitt, who has pledged to make Oklahoma the most anti-abortion state in the country.

“There can be nothing higher or more critical than the defense of innocent, unborn life,” Republican State Representative Jim Olsen said on the floor of the Oklahoma House on Thursday, where the bill passed 73-16.

The bill is modeled after a Texas law that went into effect in September, which prohibited abortion after six weeks and relied on civilian rather than criminal enforcement to work around court challenges. Because of that provision — the law expressly states that state authorities cannot bring charges — the United States Supreme Court and state courts have ruled that the ban cannot be overturned, even if it violates the constitutional right to abortion established in Roe v. Wade.

The Oklahoma law is stricter than the Texas law, which prohibits abortion after six weeks of pregnancy.

An unborn child is defined in the bill as “a human fetus or embryo in any stage of gestation from fertilization until birth.” Since the 1973 Roe v. Wade decision, anti-abortion groups have tried unsuccessfully to pass federal or state legislation defining life as beginning at fertilization.

The vote on Thursday was the latest step by Oklahoma’s Republican-led Legislature, working with Mr. Stitt, to erode abortion rights until the procedure is effectively outlawed. Together, they have propelled their state to the forefront of the pack of Republican-led states rushing to pass abortion-restricting or prohibiting legislation in the expectation that the Supreme Court will soon overturn Roe v. Wade. A draft opinion written by Justice Samuel A. Alito Jr. that was leaked, along with oral arguments in the case at hand, about a Mississippi law that prohibits the procedure after 15 weeks of pregnancy, suggested that the court was willing to do so.

Outnumbered Democrats in Oklahoma’s State House begged their colleagues not to pass the bill on Thursday. Several people urged Oklahoma to prioritize funding for family planning services or improving the lives of poor young Oklahomans.

In an exchange on the House floor with a Republican sponsor of the bill, an Oklahoma Democrat, Cyndi Munson, stated that many women, particularly young girls who may be victims of incest, do not report rape or incest to law enforcement.

Abortion opponents are increasingly relying on civilian law enforcement to achieve long-standing objectives. Even if no lawsuits are filed against abortion providers, civilian enforcement laws have had a chilling effect on abortion providers and abortion pill distributors, causing them to cease operations for fear of being sued.

Other states have attempted to prohibit abortions throughout pregnancy, but have been stopped by a court order because, according to the Roe decision, states cannot prohibit abortion before viability, or approximately 24 weeks. Mississippi, among other states, has attempted but failed to pass ballot initiatives that would define fetuses as persons, making abortion murder.

The Oklahoma bill, if signed by the governor, would eliminate another option for Texas women who had been flooding across the state border to seek legal procedures, and it seeks to punish even those from out of state who assist Oklahoma women in getting abortions.

According to the Guttmacher Institute, which advocates for abortion rights, there were 4,780 abortions in Oklahoma in 2017, the most recent year for which statistics are available. Oklahoma’s abortion rate, like that of the majority of states, had been declining. However, the Texas law resulted in a surge of women crossing into Oklahoma to obtain abortions. In the first three months after the law went into effect, Planned Parenthood’s health centers in Oklahoma saw a 2,500 percent increase in the number of patients from Texas.