More than half of Michigan voters chose to amend the state constitution to define the union of one man and one woman in marriage as the only agreement recognized as a marriage or similar union for any purpose.

Supporters of Proposal 2 said the new amendment will protect marriage at a time when it is threatened.

"The people of Michigan have spoken very strongly and very clearly that they want the institution of marriage to remain only between a man and a woman," said Gary Glenn, the president of the American Family Association of Michigan.

"There's no mistaking that tonight."

The bill was rejected by the Michigan Board of State Canvassers earlier this year, but supporters petitioned and managed to place it on the general election ballot.

Opponents of the amendment said there were laws prior to the proposal that prevented same-sex couples in Michigan from marrying, but the phrase "or similar union for any purpose" in this proposal presents a cause for alarm.

"Personally, I am disappointed that our efforts to prevent it haven't been successful," said Franny Howes, a social relations senior who is involved in the lesbian, bisexual, gay and transgender community on campus. "The potential that it has to take away rights in Michigan really scares me.

"Grassroots LBGT activists will have to work even harder to protect our rights."

Members of MSU Stonewall Democrats and Coalition for a Fair Michigan said that with the passage of the proposal, couples might lose their domestic partnership benefits. They argue this might hurt children because they could lose the health insurance coverage of their parents.

But Proposal 2 supporters said the amendment will protect family life and structure, arguing that children need a mother and a father for healthy development.

"This overwhelming vote expresses a common-sense acknowledgment by the people of Michigan that what's best for a child is to have a mother and a father," Glenn said. "Sometimes, we're short of that ideal, but for the sake of what's best for children, Michigan voters said they want to continue to uphold that ideal as something to which society should aspire."

Initiatives similar to Proposal 2 have been introduced in swing states across the country and similar amendments have been placed on the ballot in 10 other states.

The American Family Association of Michigan upholds the amendment as a way to prevent the legalization of marriage between same-sex couples.

The group holds Massachusetts - where the state Supreme Court ruled that prohibiting same-sex marriage was illegal discrimination - as a warning of what could happen in Michigan.