A Republican senator is holding up a Michigan judge's nomination to the federal bench because she reportedly helped lead a commitment ceremony for a lesbian couple in Massachusetts four years ago.

Sen. Sam Brownback of Kansas, an opponent of gay marriage who has presidential aspirations, said Friday he wants to know whether there was anything illegal or improper about the ceremony. He also said he wants to question Michigan Court of Appeals Judge Janet T. Neff about her views on gay marriage and how her actions might shape her judicial philosophy.

"It seems to speak about her view of judicial activism," Brownback said. "That's something I want to inquire of her further."

The Senate Judiciary Committee last week approved Neff's nomination for a seat on the U.S. District Court in Michigan's Western District. Her nomination is now pending before the full Senate.

A single senator can block a nomination from moving forward by placing a hold on it.

A White House spokesman did not immediately return a call seeking comment on Friday. Neff has not returned phone calls this week.

Brownback said Republican activists in Michigan expressed concerns about Neff after seeing her name in a September 2002 New York Times "Weddings/Celebrations" announcement. It said Neff led the commitment ceremony for Karen Adelman and Mary Curtin with the Rev. Kelly A. Gallagher, a minister of the United Church of Christ.

While commitment ceremonies marking the union of same-sex couples have grown increasingly common, they are largely symbolic and carry no legal benefits. Brownback said he wanted to find out whether Neff may have presided over "an illegal marriage ceremony" that skirted Massachusetts law, which did not recognize gay marriages at the time.

The state later legalized gay marriage in 2004 — the only state to do so — after a ruling from its highest court.

Sen. Carl Levin, D-Mich., who learned about the ceremony this week, said based on the newspaper announcement it didn't sound like Neff did anything illegal.

"There's no reason why two people can't stand up and exchange commitments with each other provided they don't do anything illegal," Levin said.

Brownback cited recent instances in California and New York where local officials issued marriage licenses to same-sex couples contrary to existing laws.

"I don't know what she did," Brownback said. "That's why there's a factual question."

Brownback has asked the U.S. Justice Department for a formal legal opinion in addition to asking Neff specific questions.

Neff, 61, has served on the Michigan Court of Appeals since 1989. She was nominated by President Bush in June — along with Grand Rapids attorney Robert Jonker and Berrien County Circuit Judge Paul Maloney — to fill three vacancies on the district court.

Levin said Neff was nominated along with Jonker and Maloney as part of an agreement he and Sen. Debbie Stabenow, D-Mich., reached with the White House. Brownback said Neff has a more liberal reputation while Jonker and Maloney are considered conservatives.

Bush has long advocated a ban on gay marriage. In July, a proposed constitutional amendment to ban same-sex marriage failed to win the needed two-thirds support in both the Senate and House.

Forty-five states have either constitutional amendments banning gay marriage or statutes outlawing same-sex weddings. Twenty states, including Michigan, have approved bans on same-sex marriage and eight states are considering similar measures in November.