Reasonable accommodation must be made, which means the company incurs no more then de minimus costs.

And while I don't like seeing workgroups pitted against each other, if there was an exemption carved out that gave someone weekends off for the entirety of their career, despite the requirements for the rest; let them avoid work that was universally reviled, or gain work that was universally desired; or allowed them to jump the privilege afforded by seniority/longevity in station or at the company, not only would that be a hardship paid by the rest of us, but it would encourage others to abuse it.