OKLAHOMA CITY - Two Oklahoma couples who are plaintiffs in a potentially landmark case challenging Oklahoma's ban on same-sex marriage are being honored by the American Civil Liberties Union.

The ACLU's Oklahoma chapter announced Wednesday it plans to present its Angie Debo Civil Liberties Award to the four women: Mary Bishop, Sharon Baldwin, Susan Barton and Gay Phillips.

The four women filed a lawsuit in 2004 after Oklahoma voters approved an amendment to the state constitution that banned same-sex marriage.

The plaintiffs contend the ban violates the U.S. Constitution's equal protection clause in the 14th Amendment.

"In the nearly ten years since this case was first filed, these plaintiffs have stood on the front lines in the fight to secure true equality for Oklahomans, and today their case stands to be a landmark that will be heralded for generations," said Ryan Kiesel, Executive Director of the ACLU of Oklahoma.

A federal judge in January ruled in favor of the couples, but the decision was stayed while the case is being appealed to the 10th U.S. Court of Appeals.

The award is named in honor of the writer, historian, and civil rights advocate Angie Debo, who relentlessly pursued justice in cooperation with the ACLU of Oklahoma during the late 1960′s and 1970′s.

The Associated Press contributed to this report.