In the six months since the Supreme Court struck down a federal ban on same-sex marriage, a flood of lawsuits and legislation has pushed the United States to a tipping point - and Pennsylvania this year could be the state that shifts the balance.

In 2013, the number of states (along with the District of Columbia) allowing same-sex marriage doubled, to 18. In the last month, judges struck down same-sex marriage bans in Utah and Oklahoma.

If those two rulings are upheld, nearly 46 percent of the U.S. population would live in places that allow same-sex marriage or civil unions. If Pennsylvania joins the list, it will be slightly over 50 percent.

"Clearly, the tide has turned," said Ellen Toplin of Dresher, Montgomery County, who married her partner of 22 years in July and who is suing the state to recognize that marriage.

Hers is one of at least seven lawsuits challenging Pennsylvania's 1996 marriage law, which defines marriage as between one man and one woman and doesn't recognize same-sex unions performed in other states.

The suits span federal, state, and county courts. Some challenge the law as unconstitutional on its face; others take on narrower aspects, such as the voiding of marriages from other states or the inheritance and estate taxes same-sex couples wouldn't have to pay if they were of different genders.

Similar suits are pending in almost every state that still bans same-sex marriage, but experts believe Pennsylvania may be the next to change.

John Culhane, a law professor at Widener University, said Pennsylvania is more vulnerable than most of the other states because its ban is not enshrined in the state Constitution. That means opponents can challenge the law on state and federal grounds.

The commonwealth also is unique in that it is home to 118 same-sex couples who married here but who aren't sure whether their marriages are valid.

Couples such as Toplin and her partner came from across the state to Montgomery County last summer after Register of Wills D. Bruce Hanes announced he would issue marriage licenses to gay and lesbian couples.

The licenses, and a subsequent lawsuit by the Corbett administration, sparked protests and counterprotests and drew national attention.

A Commonwealth Court judge in September ordered Hanes to stop but didn't say whether the existing marriages were valid.

"As far as we're concerned, we're married in Pennsylvania. The state, obviously, takes a different approach," said Diana Spagnuolo, who married her partner in July in their Wynnewood backyard.

That uncertainty complicates things at tax time. Spagnuolo, a partner in a law firm that operates in multiple states, has to file returns in at least eight different states - some of which allow same-sex marriage, some of which recognize out-of-state marriages, and some of which do neither.

"That's a very sticky issue. It's going to require some thought, both legal counsel and accounting counsel," she said.

After the Supreme Court struck down the Defense of Marriage Act, the IRS and other agencies issued a ruling that same-sex couples, regardless of where they now live, can file as spouses if they married in a state where it was legal.

The U.S. Justice Department went a step further for Utah, where about 1,300 same-sex weddings were completed before the Supreme Court put a hold on the lower court's ruling.

On Jan. 10, Attorney General Eric Holder issued a statement saying that as far as the federal government was concerned, those couples are married.

"These families should not be asked to endure uncertainty regarding their status as the litigation unfolds," Holder said in a video announcement.

No such clarification has come for the Pennsylvania couples. Until it does, Spagnuolo and others said, they will continue to spend hours on the phone with government agencies and lawyers, trying to figure out whether they qualify for joint taxes, spousal health care, shared pensions, Social Security, and familial rights.

The uncertainty adds an extra level of urgency to the lawsuits here. Commonwealth Court set a schedule for Spagnuolo's case last week, ordering the state to file preliminary objections by Feb. 18.

A federal case also moved forward on Monday, when attorneys for two women who married in Massachusetts filed arguments on why Pennsylvania must recognize their union.

And on Friday, the state responded to an appeal Hanes filed in state Supreme Court. State attorneys wrote that whether or not the same-sex marriage ban is constitutional, Hanes didn't have the authority to violate state law.

The state is also fighting another case in Commonwealth Court, a high-profile ACLU case in federal court - scheduled for trial in June - and at least two cases in county courts, challenging decisions on estate or inheritance tax bills.

Michael Geer, president of the Pennsylvania Family Institute, which supports the current marriage law and says a majority of voters and elected officials agree, objects to the portrayal of same-sex marriage as "a growing tide," when so many states' laws are being decided in courtrooms.

"If they're confident that public opinion is changing and it's inevitable, if you will - well, then let this process work. It's a policy decision," he said. "In essence, it's been taken out of the hands of the people of Pennsylvania."

But supporters point to the numbers and say they're optimistic.

"In a year's time, I just hope this is a nonissue in Pennsylvania. . . . I can spend my time on other things," Spagnuolo said.

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