It is given to them by the men in authority of those churches. It is totally unscriptural and they are actually very hypocritical in the way they apply it. It is rules of men in churches of men and has nothing to do with scripture. We once went to a "pch" church and our women were berated because they wore pants ( temp was 10 degrees) yet their music leader wore a mesh blouse with no bra, exposing herself , but that was not a problem to them. Rules of men have no place God's Kingdom and are only found in apostate churches led by proud men.
The scripture says dress modestly and that is all it says