The Tribal Council voted unanimously Friday in favor of the Dine Marriage Act of 2005. Dine is the Navajos' name for themselves.

The act restricts a recognized union to a relationship between a man and a woman and prohibits plural marriages as well as any marriage between parents and children, grandparents and grandchildren, brothers and sisters and other close relatives.

Supporters say the goal is to promote Navajo family values.

''Men and women have been created in a sacred manner. We need to honor this,'' said delegate Harriet Becenti.

Critics of the legislation have said its sponsor, delegate Larry Anderson of Fort Defiance, is attempting to rewrite cultural history to parallel conservative Christian backlash against gay rights across the United States.

Anderson noted Friday that ''man'' and ''woman'' are already specifically cited in the Navajo Nation Code that outlines the forms to be used for marriage licenses.

Many of the delegates said the council wasn't promoting discrimination with the passage of the act but rather strengthening tribal policy.

Delegate Lorenzo Curley said Navajo leaders want to send a message to the tribe's young people to respect and live by the Fundamental Laws of the Dine.

''We want to say to them 'Hold on fast to your society, your roots, your values,''' he said. ''We are here to defend the foundation of our society. That's what is at stake here.''

The Navajo Nation spans parts of Arizona, New Mexico and Utah. Same-sex marriages aren't allowed in any of those states.

Same-sex marriages became a national issue last year, starting Feb. 12 in San Francisco when Mayor Gavin Newsom opened the city's wedding registry to gays couples. The debate reached New Mexico later that month when the Sandoval County clerk issued licenses to about 60 same-sex couples, but the state attorney general quickly settled the matter by saying that the licenses were illegal.

In November, voters 11 states approved constitutional amendments to ban gay marriages. Voters in two other states, Missouri and Louisiana, barred gay marriages earlier in 2004.

In August, the Cherokee National Tribal Council in Oklahoma voted to define marriage as between a man and a woman after a lesbian couple filed for a tribal marriage application.