Eden Prairie has become the 18th Minnesota city to approve a domestic partner registry, but the measure passed only after a debate about whether the plan represented an affront to marriage.

City Council Member Brad Aho cast the sole vote against the registry, calling it inappropriate and "a big change in direction for the city."

"This ordinance undermines our society being based on marriage and infers that any relationship is equal to marriage between one man and one woman," he said during a council meeting last week. Such a measure should be voted on by city residents, he said, adding that it was unwise to tackle such a proposal before Minnesotans vote on the marriage amendment on the ballot in November.

But other council members said a domestic registry was in synch with the "Eden Prairie Manifesto," a city document that spells out goals of tolerance and nondiscrimination.

"I do think all of us up here understand the political environment we are discussing this in," said Council Member Ron Case. "It's not about sanctioning or licensing. ... For me, it's about personal freedom and family values and civil rights."

The ordinance allows unmarried couples in committed relationships to document their relationship by registering with the city and paying $20 to cover administrative costs. While some Minnesota cities have offered the service to people who live or work within their borders, Eden Prairie is limiting the registry to couples who live in the city. The registry was proposed by the city's Human Rights and Diversity Commission.

Though domestic registries have been criticized as toothless -- state law prohibits local governments from offering health benefits to domestic partners -- advocates say they have real benefits. For example, couples can qualify for family rates at city recreational facilities and use their registry documents to apply for insurance benefits with employers that recognize domestic partners. Or they can use the registry to prove their committed relationship to hospital officials when important medical decisions need to be made.

Mayor Nancy Tyra-Lukens said she had received only one phone call and three e-mails opposing the measure and 12 e-mails in favor, which she thought was unusual. One writer had a 76-year-old mother who had lived with a man for years in a committed relationship but did not want to marry. Another correspondent was an Iraq war veteran who lives with a same-sex partner.

"These young men and women who fought for our country and other countries, do we want them in our city? Yes, we do," Tyra-Lukens said. "At the end of the day, I don't see any impact on ... the validity of marriage.

"I just really feel this is the right thing to do."

Four of the five council members agreed. The ordinance takes effect Thursday.

Minneapolis was the first Minnesota city to establish such a registry, passing its ordinance in 1991. Duluth and St. Paul approved registries in 2009, followed by Rochester, Edina, Maplewood and Golden Valley in 2010, Shoreview, Falcon Heights, Robbinsdale, St. Louis Park, Hopkins, Shorewood, Red Wing, Crystal, Richfield in 2011, and Eagan earlier this month.

Mary Jane Smetanka • 612-673-7380 Twitter: @smetan