North Carolina already has a law barring same-sex marriage, but the state’s Republican-controlled Legislature is not satisfied. It devised a measure to enshrine this obvious discrimination in the State Constitution and placed it on the ballot of the state’s May 8 primary election — a test of tolerance versus bigotry that ought to be watched closely nationwide.

In their zeal, lawmakers got careless with the wording of the measure, known as Amendment One. It would constitutionally prohibit recognition not just of same-sex marriages, but of other legal arrangements like civil unions and domestic partnerships. That could harm all unmarried couples, imperiling some children’s health insurance benefits, along with child custody arrangements and safeguards against domestic violence.

The campaign against the amendment is being spearheaded by a coalition of civic, religious, business and civil rights leaders and groups. One of Amendment One’s most vocal opponents is the Rev. William Barber II, president of the state chapter of the N.A.A.C.P. Mr. Barber draws a strong link between the proposed amendment and struggles against racial unfairness, an appeal with special resonance following the publication in March of memos from the National Organization for Marriage, one the most prominent groups fighting same-sex marriage, about driving “a wedge between gays and blacks.”

Polls suggest that defeating this measure remains an uphill struggle, but at least its approval is no longer an entirely foregone conclusion. Much will depend on turnout, especially by voters on college campuses, who will need to vote in larger-than-usual numbers to defeat this declaration of officially sanctioned discrimination.