JEFFERSON CITY, Mo. — The Missouri Supreme Court upheld a law yesterday letting parents sue people who help their teenage daughters get abortions without their consent.

The court’s unanimous decision in Planned Parenthood v. Nixon rejected claims by Planned Parenthood that the 2005 law could infringe on their free-speech rights to provide information and counseling about abortions. It also turned down various other constitutional challenges by the organization.

The law states that “no person shall intentionally cause, aid, or assist a minor to obtain an abortion without the consent” of a parent or court. Parents and guardians can sue those who violate the law, seeking compensation for emotional injury and punitive damages.

A Jackson County judge had expressed “substantial trepidation” while upholding the law in November 2005, and had issued an injunction against enforcing it pending an appeal to the Missouri Supreme Court.

Attorney General Jay Nixon’s office, which defended the law, said it immediately took effect yesterday as a result of the Supreme Court’s ruling.

Planned Parenthood affiliates had argued that the words “aid” and “assist” could be applied broadly to prohibit abortion counseling or the sharing of information.

The Supreme Court applied a more narrow interpretation, ruling that those specific things weren’t prohibited and the law did not violate the First Amendment right to free speech.

A Planned Parenthood executive expressed satisfaction with that part of the ruling, even though the Supreme Court did not grant its request to strike down the law.

“We’re pleased that the court has upheld our ability to provide information and counseling, because that is what patients of any and all ages expect from us,” said Paula Gianino, president of Planned Parenthood of the St. Louis Region.

Missouri Right to Life, which had helped write the law, said it was never intended to target mere speech but rather actions, such as providing money or transportation for a minor to get an abortion at an out-of-state clinic without permission from her parents. Missouri’s original parental-consent law was upheld by the U.S. Supreme Court in 1983.

“This law was written to really protect the rights of parents,” said Patty Skain, executive director of Missouri Right to Life. Otherwise, “minors will go out of state — and, in a way, almost be lured out of state — and not have the benefits of having their parents there to help them in that decision.”

The legislative impetus for the law came from the Hope Clinic for Women in Granite City, Ill. — just across the border from St. Louis — which had advertised Illinois’ lack of a parental-consent law for abortions. After Missouri legislators adopted the civil-liability law in a special session, the Hope Clinic quit performing abortions on Missouri minors who did not have parental consent.

The Supreme Court rejected a claim that the law violated the commerce clause to the U.S. Constitution by essentially requiring clinics in other states to comply with Missouri’s parental-consent requirements. Out-of-state abortion clinics that follow their own state laws cannot be held liable for damages under Missouri’s new law.

The court also rejected Planned Parenthood’s claims that the law imposed an undue burden on minors to obtain an abortion and violated their “right to travel.”

Republican Gov. Matt Blunt praised the court’s decision as a “victory in our efforts to establish a culture that values all human life.”

“Parents must be informed of their children’s decision to end an innocent life, and today’s ruling upholds that belief,” Blunt said in a written statement.