– The Texas Supreme Court on Friday said that while same-sex marriage is legal nationwide, the "reach and ramifications" of the rights of gay couples have yet to be determined.

In a unanimous decision, the court reversed a lower court's ruling in favor of the city of Houston's decision to extend spousal benefits to same-sex city employees and their married partners. The court ordered the case sent back to the trial court.

The high court conceded that the U.S. Supreme Court legalized same-sex marriage two years ago in Obergefell vs. Hodges, but added that it is unclear what other rights the decision extends to same-sex couples. That must be hashed out in cases like this one.

Conservative groups hailed the ruling as protecting traditional marriage, while those fighting for the rights of lesbian, gay, bisexual and transgender Americans called it an attempt to "undercut" rights.

"The Texas Supreme Court's decision this morning is a warning shot to all LGBTQ Americans that the war on marriage equality is ever-evolving," Sarah Kate Ellis, president of the national group GLAAD, said Friday.

The case dates to 2013, when two local taxpayers sued then-Houston Mayor Annise Parker, the city's first openly gay mayor. Relying on a legal opinion from the city attorney, Parker had decided to extend spousal benefits to gay couples, even though an amendment to the city ­charter banned the practice.

Jack Pidgeon, a pastor, and Larry Hicks, an accountant, sued Parker, arguing that no city employees have a "fundamental right" to receive government-subsidized spousal benefits and that it was "perfectly constitutional" to give benefits to some married couples and deny them to others.

When Obergefell was decided 18 months later, the state of Texas and government-funded entities, like universities, began extending spousal benefits to same-sex couples in their employ. But conservative groups continued to fight the city of Houston's decision.

The Texas Supreme Court initially refused to hear the Houston case. But after pressure from the top elected Republicans in the state, including Gov. Greg Abbott, the court made the unusual decision to reopen the case.

On Friday, the state Supreme Court said the Obergefell ruling did not detail what rights, other than marriage, are guaranteed to same-sex couples.

Litigants "must now assist the courts in fully exploring Obergefell's reach and ramifications, and are entitled to the opportunity to do so," Justice Jeffrey Boyd wrote.