A federal judge on May 13 struck down the ban, saying the measure was too broad and deprived gays and lesbians of participation in the political process.
U.S. District Judge Joseph Bataillon said the amendment interferes not only with the rights of gay couples but also with foster parents, adopted children and people in a host of other living arrangements.
Seventy percent of Nebraskans approved the amendment in 2000.
The judge's ruling did nothing to change the status of gay marriage (search) in Nebraska. It was not allowed before the ban's adoption and it remains against the law.
While it specifically banned gay marriage, it went further than similar bans in many states by prohibiting same-sex couples from enjoying many of the legal protections that heterosexual couples enjoy. Gays and lesbians who work for the state or the University of Nebraska system, for example, were banned from sharing health insurance and other benefits with their partners.
Bruning had promised an appeal when Bataillon's decision was released last month.
In a brief statement Thursday, Bruning said the case would be vigorously pursued.
"We look forward to having another day in court and defending Nebraskans' right to amend their constitution as they see fit," he said.
The case will be considered by the 8th U.S. Circuit Court of Appeals, which is based in St. Louis. No date for arguments has been set.
The lawsuit challenging the ban was filed by New York-based Lambda Legal and the ACLU's Lesbian and Gay Project.
David Buckel, senior staff attorney at Lambda Legal, said the appeal was expected.
"We're hopeful, because the law that Judge Bataillon struck down is the most extreme anti-gay family laws in the nation," Buckel said Thursday.
Forty states have so-called "Defense of Marriage" (search) laws.
The Nebraska Family Council led the petition drive to get the ban on the ballot.
Al Riskowski, executive director of the group, said he expects the decision to be overturned on appeal.
"We are delighted that the state of Nebraska recognizes the importance of upholding the traditional definition of marriage," Riskowski said. "It's so important to us as a state and a country. If the definition of marriage would potentially be changed, what we teach our children about marriage and family would radically change."
Opponents of gay marriage, including Riskowski, have pointed to the May ruling as a reason to seek a national ban.
In the May ruling, Bataillon said Nebraska's ban "imposes significant burdens on both the expressive and intimate associational rights" of gays and lesbians and "creates a significant barrier to the plaintiffs' right to petition or to participate in the political process."
Buckel of Lamda Legal said opponents of the ban were not seeking the legalization of gay marriages in Nebraska.
"We're just asking for the rights of our families to be able to advocate for protections for those families from the Legislature," he said.
Bataillon said the ban amounted to punishment by going beyond merely defining marriage as between a man and a woman, noting that it also says the state will not recognize two people in a same-sex relationship "similar to marriage."
The judge also said the amendment's "broad proscriptions could also interfere with or prevent arrangements between potential adoptive or foster parents and children, related persons living together, and people sharing custody of children as well as gay individuals and people inclined to align with them to promote changes in legislation."