The American Civil Liberties Union launched a legal challenge Tuesday to Pennsylvania’s ban on gay marriage, part of a flurry of lawsuits filed since last month’s U.S. Supreme Court ruling on federal benefits for same-sex couples.

In the lawsuit filed in Harrisburg, Pa., the ACLU is representing 23 plaintiffs: 10 gay couples, two children of one of the couples, and the surviving partner in a same-sex couple who were together for 29 years.

James Esseks, who directs the ACLU’s Lesbian Gay Bisexual Transgender & AIDS Project, said the group hopes to secure the right for gay couples to marry in Pennsylvania, force the state to recognize same-sex marriages performed elsewhere, and increase pressure on the Supreme Court to ultimately rule on whether same-sex marriage should be legal across the nation.

“Pennsylvania recognizes straight people’s marriages from Maine and New York, but it doesn’t recognize gay people’s marriages from Maine and New York,” Esseks said. “The question is, why?”

Opponents of same-sex marriage questioned why activists were seeking redress in court rather than through a ballot initiative in Pennsylvania. Under Pennsylvania law, the state legislature has to approve resolutions before they can be put on the ballot for a direct vote, and no resolution endorsing gay marriage has passed at this point.

“We think it’s very telling that gay-marriage advocates are using the courts so heavily,” said Thomas Peters, communications director for the National Organization for Marriage. “They only support the voice of the people when they think it will go their way.”

Peters said his group is focused on Indiana, where Republican Gov. Mike Pence has urged the legislature to pass a constitutional amendment banning same-sex marriage so it can be put before the voters as a ballot initiative in 2014. The organization is also involved in an ongoing legislative fight in Illinois over whether to legalize gay marriage there.

Meanwhile, a pro-gay-marriage group called Freedom to Marry announced Tuesday that it would spend $500,000 on state initiatives to legalize gay marriage, including $250,000 on an effort to reverse Oregon’s ban through a ballot initiative next year. The group said it had hired Richard Carlbom, who spearheaded the successful effort to legalize gay marriage in Minnesota, as its director of state campaigns.