People distribute signs supporting the Right to Abortion Initiative at a rally in Bozeman, Mont., on Sept. 5.William Campbell / Getty Images file

Montana voters approved a ballot measure enshrining abortion in the state constitution, NBC News projects, delivering a victory to advocates for reproductive rights in a Western red state.

The amendment will not change current law on abortion in Montana: Abortion is legal in the state until fetal viability, around the 23rd or 24th week of pregnancy, backed up by a 1999 ruling by the state Supreme Court.

But advocates for the ballot measure wanted to guard against potential changes by the Legislature or state Supreme Court justices in the heavily Republican state.

The amendment establishes a right for people to "make and carry out decisions about one's own pregnancy," including the right to abortion; prohibits the government from "denying or burdening" the right to abortion before fetal viability; and bars the government from "denying or burdening access" to abortion when a health care professional determines it is "medically indicated to protect the pregnant patient's life or heath," according to the ballot language.

The measure also prevents the government from "penalizing patients, healthcare providers, or anyone who assists in exercising their right to make and carry out voluntary decisions about their pregnancy."

The ballot measure required a simple majority to pass. It withstood a series of legal challenges from Republicans in the solidly conservative state.

Nine other states considered constitutional amendments concerning abortion rights in this election: Arizona, Colorado, Florida, Maryland, Missouri, Nebraska, Nevada, New York and South Dakota.