While a handful of courts around the United States have found unconstitutional President Trump’s travel ban on Muslim-majority nations, these courts may have overlooked an important point, says an expert on law and religion at Washington University in St. Louis.

“Courts across the country have rightly concluded that the Muslim travel ban is unjust and unconstitutional,” said Elizabeth Sepper, associate professor of law.

“But they haven’t always recognized a key principle — that the First Amendment forbids the government from acting based on animus toward religion in general or a particular religious group.”

Sepper, along with a group of leading constitutional law scholars from throughout the country, has filed an amicus brief in the U.S. Court of Appeals for the 4th Circuit, which is hearing the case International Refugee Assistance Project v. Trump.

“Given all of President Trump’s public promises of a Muslim ban, it is hard to imagine a clearer case of governmental action motivated by animus toward a single religion than the executive order here,” Sepper said. “This act of hostility and prejudice toward a religion cannot stand under the First Amendment of the Constitution.”

“The Supreme Court has warned in the strongest terms against governmental action based on animus toward religion,” states the brief. “Given the centrality of religion in many people’s lives — to their identity, social relations, and concept of the universe — there is good reason to look with the utmost doubt upon official acts based on hostility to religion in general or any particular religion.”

The brief, supported by constitutional scholars with a wide diversity of views about the First and 14th Amendments, will be useful to the courts as they hear argument in the coming months, Sepper said.