Sen. Barbara Mikulski (photo courtesy wikimedia)

The senior U.S. senator from Maryland is facing increasing pressure to sign on as a co-sponsor of legislation to repeal the Defense of Marriage Act amid plans to win marriage equality in her state in 2012.

A coalition of LGBT rights advocates — made up of Courage Campaign, Freedom to Marry and Equality Maryland — are building pressure on Sen. Barbara Mikulski (D-Md.) to co-sponsor the Respect for Marriage Act by circulating a petition among Maryland residents asking her to support the bill.

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As of Tuesday, organizers had collected more than 3,000 names for the petition encouraging Mikulski to voice support for the Respect for Marriage Act. LGBT rights advocates were set to deliver the petition to Mikulski’s Baltimore, Md., office on Friday.

LGBT rights advocates said Mikulski’s lack of co-sponsorship of the bill, which is sponsored by Sen. Dianne Feinstein (D-Calif.), is particularly striking because other elected officials in her states have voiced support for same-sex marriage and because plans are in motion to legalize same-sex marriage in the state next year.

Rick Jacobs, chair of the Courage Campaign, said Mikulski’s support would be significant because she’s a leader of the Democratic Party and because it would align her with the movement toward marriage equality in Maryland.

“I think with Sen. [Benjamin] Cardin on board, and the governor on board and her state moving, I think it’s really important that she joins in,” Jacobs said. “I’m going to assume that her staff and she simply need education. I’m going to assume that. If several thousand of her constituents can help her provide that education, then that’s great. But beyond that it’s really time for Sen. Mikulski to join us.”

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Last month, Gov. Martin O’Malley announced he would push for the legalization of same-sex marriage in Maryland as part of his legislative package in 2012. The Maryland governor had been criticized for not taking a leadership role in the effort to legalize gay nuptials in his state this year.

Evan Wolfson, president of Freedom to Marry, said O’Malley’s support indicates that Maryland is in the midst of a debate on same-sex marriage and said Mikulski’s co-sponsorship of the Respect for Marriage Act would show where she stands in the discussion.

“It’s important that Sen. Mikulski be on the right side of this deeply important matter of justice for families and the right side of history as well,” Wolfson said.

Additionally, Wolfson said Mikulski’s co-sponsorship would put her in a position to back same-sex couples in her state who are married or are seeking the right to marry. While Maryland doesn’t offer same-sex marriage under state law, it recognizes such unions that are performed in other jurisdictions.

“As we’ve seen from the release on Census data and the snapshots provided by the Williams Institute and others, there are families in Maryland across the state who are harmed by the denial of marriage, and by federal discrimination against the marriages that they manage to celebrate right across the border in the District of Columbia as well as other states,” Wolfson said.

According to recent numbers published by the Williams Institute at the University of California in Los Angeles based on data from the 2010 U.S. Census, 16,987 same-sex couples live in Maryland and make up 7.88 couples in every 1,000 households.

Rachel MacKnight, a Mikulski spokesperson, said the senator is “very closely” looking at Feinstein’s legislation.

As long as the Senate is out of session for August recess, Mikulski is unable to sign on as a co-sponsor to the legislation. An informed source said the senator would make an announcement regarding her support for the Respect for Marriage Act in September.

Other members of the congressional delegation from Maryland have already signed on in support of the legislation. Cardin, the junior senator from Maryland, joined on as a co-sponsor in May. The legislation has a total of 28 co-sponsors in the Senate — all Democrats.

In the House, where Rep. Jerrold Nadler (D-N.Y.) sponsors companion legislation, Reps. John Sarbanes, Donna Edwards and Chris Van Hollen as well as House Minority Whip Steny Hoyer have become co-sponsors. The House legislation has 120 co-sponsors in total.

Lisa Polyak, acting board chair for Equality Maryland, said support from Mikulski would “round out the complement” of statewide elected officials in Maryland who’ve voiced support for same-sex marriage.

“She’s the only one at this time who doesn’t, both at the state and federal level,” Polyak said. “I think there’s really no reason for her not to support it. Public opinion polls are there. She’s shown herself to be a progressive senator on other issues, and I think this fits easily within the types of issues that she’s supported in the past for women and family and children.”

Other members of the congressional delegation from Maryland have yet to sign on in support of the Respect for Marriage Act. They include Democratic Reps. C.A. Dutch Ruppersberger and Elijah Cummings. Republican House members Roscoe Bartlett and Andrew Harris also aren’t DOMA repeal co-sponsors. Bartlett has voiced opposition to same-sex marriage and has voted for a U.S. constitutional amendment restricting marriage to one man, one woman.

CORRECTION: An earlier version of this article incorrectly identified Rep. Andrew Harris (R-Md.) as a Democrat. The Blade regrets the error.