A federal judge on Monday ruled Nebraska's ban on gay marriage unconstitutional in a decision that could allow same-sex couples to marry in the state within a week.

U.S. District Judge Joseph Bataillon issued a preliminary injunction in the case brought by seven same-sex couples in the state, calling Nebraska's ban an "unabashedly gender-specific infringement of the equal rights of its citizens."

Bataillon denied a state request to stay his decision but said his injunction would take effect on March 9 to assuage Nebraska officials' concerns of possible administrative turmoil.

The Nebraska Attorney General's Office was studying the decision and was expected to have a statement later.

Nebraska voters in 2000 adopted a state constitutional amendment that defines marriage as only between one man and one woman and does not recognize civil unions, domestic partnerships or similar relationships for same-sex couples.

The plaintiffs include Sally Waters, who has stage four breast cancer that has spread and wants Nebraska to recognize her 2008 marriage to Susan Waters in California in part to provide critical financial protections for their children.