Supporters say that has created a glaring contradiction in how gays and lesbians are treated by the government.
"There is definitely a synapse connection problem," said Fred Sainz, vice president of communications and marketing at the gay-rights advocacy group Human Rights Campaign.
The irony is that ENDA, as the anti-discrimination bill is often called, was long thought by supporters to be an easier goal than same-sex marriage or allowing gays to serve openly in the military.
Activists have different explanations for why it has stalled.
Felipe Sousa-Rodriguez, co-director of the gay-rights group GetEQUAL, said one problem is that polls show many Americans think that a law protecting gays and lesbians at work is already on the books.
"I don't know any other issue in this country that had this broad kind of acceptance," he said. "It shouldn't be controversial, but D.C. makes it controversial."
Grassroots support is critical for a social movement, he said, and the gay-rights movement is just beginning to grow roots.
Many trace the gay-rights movement back to the infamous Stonewall riots, which occurred after police raided a gay bar in New York City in 1969. But activists say that public support came about more recently as more and more people came out of the closet.
Today, nine out of every 10 Americans say they have gay acquaintances. A little more than half of Americans support federal benefits for gays and want to see same-sex marriage legalized for the whole country, according to March and July Gallup polls.
Even still, organizers haven't quite figured out how to harness that support into legislative action.
"I don't know that we've hit yet that secret formula that will result in enduring legal protections," Sainz said.
That's because the federal government is about a decade behind American culture — another reason ENDA hasn't become law, said Ian Thompson, a legislative representative for the American Civil Liberties Union, who urged patience among supporters.
"Particularly when you're dealing with civil rights laws, these do not happen overnight," he said.
But Sousa-Rodriguez of GetEQUAL, an organization that is often critical of mainstream gay-rights advocacy strategies, said advocates are just as behind the times as the government is when it comes to arguing for equality.