The Fifth Circuit on Monday seemed torn over whether it should "split hairs" between religious conduct and religious belief as it weighed whether to uphold a Southwest flight attendant's win in a wrongful termination suit over graphic anti-abortion messages she sent her union president.

Shay Dvoretzky of Skadden Arps Slate Meagher & Flom LLP, counsel for Southwest Airlines Co., told the Fifth Circuit that Charlene Carter's firing in 2017 stemmed from the practice of sending graphic messages to her union president, not the religious beliefs underlying those messages. The jury was therefore only required to answer whether Southwest's accommodations of that practice "would cause Southwest undue hardship," he argued.

"The distinction is critical," Dvoretzky told the court. "As a matter of common sense, belief is what's in your head. It's what you think. Practice is what those thoughts or feelings lead you to do. It's your conduct. If every practice-based claim could simply be reasserted as a belief-based claim, then undue hardship could never be a defense."

Dvoretzky said while an employee can assert both belief and practice discrimination claims, they'd have to prove different elements in order to establish both. In this case, Carter didn't provide enough evidence to prove that she was fired because she is Christian, Dvoretzky said.

But Carter's attorney Matthew Brandon Gilliam of National Right to Work Legal Defense Foundation pointed to a "fact-finding" hearing Southwest conducted after the union's president reported the Facebook messages Carter had sent her.

"She [Carter] told them, 'I'm a Christian, I'm a conservative and I'm pro-life,'" Gilliam said. "Motive is especially easy to infer when the employer knows about the religious belief before he fires her."

When the judges pressed Gilliam on where the line was between conduct that's religious and conduct that's potentially offensive, Gilliam said that Southwest's investigation into Carter's posts went beyond what she sent her union president in private.

"The difference is that Southwest went digging on Carter's website to prosecute her personal Facebook," Gilliam said, acknowledging that some of the posts sent to the union president were duplicative of ones she posted on her public page.

Drawing a line between whether the posts constitute religious conduct or religious belief may be going too far, Gilliam said, since in Carter's case, the two are closely related.

"There was a lot of testimony in the record where she talks about how she formed these religious beliefs. She talks about how she herself had an abortion and that God forgave her and she practices her religion by going out and spreading the word that abortion is the taking of human life," Gilliam said. "I think that there could be a little bit too much hairsplitting because there is a lot of interlay."

Carter sent the messages at issue to her union president in 2017 to express her opposition to the use of union funds to help members attend that year's Planned Parenthood-sponsored Women's March in Washington, D.C. She called the president "despicable," said abortion was murder and sent a video that allegedly showed aborted fetuses, according to court documents.

Carter sued Southwest and the union, Transport Workers Union of America Local 556, later that year, claiming the union retaliated against her under the Railway Labor Act and discriminated against her based on religion in violation of Title VII of the Civil Rights Act.

A jury found in favor of the longtime flight attendant after a weeklong trial, additionally finding that the union failed to represent her. A judge cut her damages award from around $5 million to $800,000, required her to be reinstated and ordered several of the airline's in-house lawyers to attend religious bias training.