. Your religion or lack thereof is a protected class under federal law and presumably Tennessee state law. The policy has a disparate impact on non-fundamentalist Christians and most non-Christians, and is therefore unlawful.
https://www.justice.gov/crt/fcs/t6manual7
Not to mention, if the plaintiffs prove their case that the policy isn’t enforced equitably between the sexes, then it’s sex discrimination too.
Not to mention, if the plaintiffs prove that it’s a ruse to circumvent protections for pregnant women, then it’s unlawful once again