Later this morning, the state ACLU will file a federal lawsuit on behalf of some two-dozen plaintiffs seeking to overturn Pennsylvania's ban on same-sex marriage.

The lawsuit -- a copy of which can be read here -- argues that a 1996 state law defining marriage as being solely between one man and one woman is unconstitutional.

"Neither tradition nor moral disapproval of same-sex relationships or marriage for lesbian and gay couples is a legitimate basis for unequal treatment of same-sex couples under the law," the lawsuit argues. It seeks to compel the state to issue marriage licenses to same-sex couples, and to recognize the validity of such unions consecrated in other states.

For the plaintiffs -- several of whom are from Pittsburgh -- such recognition is long overdue. "We've lived a married life," says Fredia Hurdle, who lives with her partner Lynn Hurdle in Pittsburgh's Crafton Heights neighborhood. The two have been in a 20-plus-year relationship, consecrated with a commitment ceremony in 2009. They have raised Lynn Hurdle's daughter, and cared for other family and friends. And now, says Fredia, they want "the acknowledgement of being married."

The state's failure to make that acknowledgement comes with a real cost. Without a government-sanctioned marriage, neither of the Hurdles is entitled to Social Security benefits if the other dies. Neither can sue an employer if the other is killed in a workplace accident. The lawsuit spells out a host of other penalties imposed on same-sex couples, including the inability to make medical decisions for an incapacitated partner. But there are also "less tangible" considerations, the suit argues, including "the message that they are less worthy and valued than families headed by opposite-sex couples."

The ACLU's lawsuit comes in the wake of a landmark Supreme Court decision handed down last month, United States vs. Windsor. In that case, US Supreme Court Justice Anthony Kennedy argued that the federal Defense of Marriage Act -- which barred the federal government from recognizing same-sex marriage -- was unconstitutional. DOMA essentially barred same-sex partners from receiving tax and other benefits federal law grants to married couples -- even if the same-sex couple had been duly married by a state that allowed it. "[T]he principal purpose and the necessary effect of this law are to demean those persons who are in a lawful same-sex marriage," Kennedy wrote. "And it humiliates tens of thousands of children now being raised by same-sex-couples."

The ACLU's lawsuit, not surprisingly, borrows from Kennedy's opinion. "[T]he Supreme Court has made clear that the law cannot ... give effect to private biases," it argues. And it contends that, if Congress was wrong to pass DOMA, Harrisburg officials were wrong to pass Act 124, the measure barring same-sex unions in Pennsylvania. Just as in Congress, the suit argues, what motivated legislators was little more than prejudice and outmoded beliefs; it quotes representatives contending, for example, that "This is a vote about family values and traditional beliefs."

But Kennedy's rhetoric, arguably, outstripped his opinion's reach. His ruling requires the federal government to honor marriages consecrated in states that allow same-sex unions. But it doesn't obligate the states themselves to issue marriage licenses to those couples. Much of Kennedy's opinion, in fact, invokes the rights of states to set the rules for marriage: In Windsor, he insisted that the federal government defer to states that permit such marriage. But would the same logic require Kennedy to defer to states that don't permit such marriage?

For couples who were married in one state but live in another, that question has added uncertainty to continuing injustice: Different marriage-related federal benefits are governed by different rules. In some cases, a couple's marital status is determined by the state where their marriage was consecrated; in others, the definition is set by the state where the couple actually resides. And changing some of those rules would require an act of Congress -- which given the make-up of the Republican-led US House is unlikely to make updating those rules a priority. As our Lauren Daley reported just last week, the result is a Pandora's Box of legal questions.

That's why, from almost the moment Kennedy's ruling was handed down, advocates on both sides of the issue expected follow-up litigation. The case being filed today is the first in the wake of Windsor. "We like to be ahead of the curve, says Vic Walczak, legal director of the Pennsylvania ACLU.

Walczak says the lawsuit takes two tacks. On the one hand, it argues that gays and lesbians should be considered a "protected class" -- a legally defined group who are entitled to special consideration because of historic prejudice against it. When laws affect such classes, courts are allowed to review those measures with "heightened scrutiny" -- a tougher standard. But Walczak says that even if the court declines to consider sexual orientation as a special category (the way it considers race) "There's still no justification for this kind of discrimination. There's no rational basis for banning same-sex marriage."

The lawsuit, for example, observes that Pennsylvania already allows adoption by same-sex couples, and that judges "routinely grant adoptions to same-sex couples, recognizing that the adoptions are in the best interest of the child." (One of the couples filing the suit, in fact, has adopted children.) Thus, the suit argues, "Any assertion that the Commonwealth does not consider same-sex couples equally effective parents cannot be credited given its own conduct."

"I think Kennedy just couldn’t quite wrap his mind around the concept that marriage is a constitutional right," says Walczak. Even so, he says, the majority opinion "comes awfully close to affirming what we need." And with polls showing gay-marriage becoming increasingly accepted -- even in famously hidebound Pennsylvania -- Walczak says "we're hoping to ride the wave of public opinion [in favor of marriage equality]. When this case is ripe for Supreme Court review in three or four years, it wouldn't surprise me if Justice Kennedy gets there."

The Hurdles hope that's true, and their personal history gives them some reason to believe it will be. Fredia Hurdle is black, and grew up in Virginia -- the very state whose laws barring interracial marriage were deemed unconstitutional by another Supreme Court ruling, 1967's Loving v. Virginia. The stakes now are really no different, she says: equality before the law, and in the eyes of their community.

"We don't want to be known as lesbians, or the lesbian interracial couple," she says. "We want to be recognized for what we are: the family next door."

I'll have more on the Hurdles, and the ACLU suit, in tomorrow's print edition.