This was true 20 years ago (not sure about now). As an atheist/agnostic in basic training I used to try different church services to get away from the barracks on Sundays. If you didn’t you were definitely assigned some cleaning detail instead of having down time. At the time it didn’t come across as discrimination and felt more like a way to keep control. At various times when control was lax bad stuff happened, e.g. fighting, sex, awol, etc. In a new light this does seem like it has a disparate impact.