COLUMBUS, Ohio (AP) — Attorney General David Yost says the state will “vigorously” defend Ohio’s restrictive abortion law from a court challenge.

Yost argues the law is objective because it sets the standard at when a doctor can hear a heartbeat, instead of viability.

Doctors say a detectable heartbeat can come as early as five or six weeks into pregnancy, before many women know they’re pregnant.

Planned Parenthood and Ohio abortion clinics sued Wednesday to prevent the law from taking effect. They argue it is unconstitutional and would prohibit nearly all abortions in Ohio.

The legal challenge was expected by the law’s backers, who are using it as part of a national anti-abortion strategy to challenge the U.S. Supreme Court’s 1973 Roe v. Wade ruling legalizing abortion.