The American Civil Liberties Union and the Council on American-Islamic Relations are appealing Oklahoma's amendment barring state courts from considering or citing Islamic Sharia law when deciding cases.
"The state of Oklahoma makes no attempt to defend the practice of singling out one religious faith for official condemnation and disability," the appellate brief read. "Nor could it."
"Barring courts from considering international law is not only constitutionally problematic, but it is also unwise and counter-productive," Jamil Dakwar, director of the ACLU Human Rights Program, said in a statement.
"The U.S. can hardly be taken seriously as a leader of global human rights, or even free trade, if states are permitted to disregard international law," he reasoned.
The move comes one year after Muslim activist Muneer Awad filed a lawsuit, saying the law was a violation of the Muslims' First Amendment rights.
State attorneys say that Awad has not shown how the proposed amendment negatively affects his Muslim faith.