JEFFERSON CITY, Mo. (AP) – In a vote watched closely by national groups on both sides, Missouri voters solidly endorsed a state constitutional amendment banning same-sex marriage.

The amendment garnered 71 percent of the vote, according to complete but unofficial results.

Missouri was the first state to consider placing the restriction in its constitution since Massachusetts’ high court ruled last year that same-sex couples have the legal right to marry in that state.

At least nine other states will consider a similar amendment this year, one as early as September. Another three states have initiatives pending.

Supporters of the ban said the amendment’s success in Missouri sends a strong signal to campaigns in other states and to Congress that the issue is of great importance to voters.

Missouri, like many states, already has a state law defining marriage as only between a man and a woman. The law specifically does not recognize same-sex marriages, even if they are performed in a state where they are legal.

But amendment supporters cited a fear that a court could toss aside the state law, and believed the state policy would be on firmer legal ground if it is ensconced in the Missouri Constitution.

The amendment states: “That to be valid and recognized in this state, a marriage shall exist only between a man and a woman.”

“I think it sends a very positive message to people in other states who are trying to protect traditional marriage there,” said Vicky Hartzler, a former Republican lawmaker and spokesperson for the Coalition to Protect Marriage in Missouri. “It says that people of this country value traditional marriage and they want to see it protected from judicial activism.”

Opponents, meanwhile, said they will turn their focus to helping campaigns elsewhere and making strides for the GLBT community in other areas.

Doug Gray, campaign manager for the Constitution Defense League, said he planned to share campaign strategies with groups fighting similar amendments elsewhere.

“We’re already reaching out to these other states, sharing with them what we learned, what worked, what didn’t work, and we’ll move on. … Ultimately we’re right and they’re simply wrong,” he said.

Gray also said the group would reach out to those who opposed the amendment and work together on issues important to Missouri’s GLBT community, such as protection from employment discrimination.

“We’ll take what we have built and communicate with them and say, ‘Let’s elect people that want to focus on the real issues,’” he said.

Even with passage, an opponent could challenge the amendment as conflicting with the federal Constitution’s due process and equal protection clauses. But Gray said he’s not planning a court challenge at this time.