WASHINGTON, DC—The stage was set Tuesday for another face-off over the rights of same-sex couples to  marry, this time in the nation’s capital, as members of the D.C. City Council introduced legislation that would formally legalize the practice.

If passed—as many expect—Washington would become the first truly southern city to allow such unions, a fact that opponents will surely use to galvanize opposition in the month to come.

In May, D.C. passed a law that recognized same-sex marriages performed in other jurisdictions, preparing the ground for complete recognition and acceptance, an evolution that has come with a price.

According to the New York Times, “For the city, the issue has stirred race and class tensions, as most of the vocal opponents represent black churches, while the more liberal and white population largely backs the measure.”

Currently, same-sex marriage is legal in Connecticut, Iowa, Massachusetts and Vermont; New Hamshire begins allowing the practice next year and Maine has an initiative on the November ballot. Many other states have begun discussion—if not proceedings—that indicate a definite trend manifested at the local and state level toward the allowance of a practice that a few years ago seemed all but moribund.

As difficult as it is to see a state law through to completion, however, D.C. faces it’s own unique challenges. Even if the current measure is passed by the council and then signed into law by the mayor, who supports it, it still has to be approved by Congress, which may have other ideas.

“The measure is likely to draw harsh criticism from Congressional Republicans and conservative Democrats, many of whom face midterm elections next year, and they could act to overturn it,” warns the Times. “Congress has 30 days to enact a joint resolution of disapproval. President Obama would have to sign that resolution for the city law to be blocked.

“But even if, as most gay rights advocates predict, such a resolution is not passed, members of Congress could still try to attach a rider to another piece of legislation blocking same-sex marriage here.”

The bill is expected to become law by December.