No one has probably thought of denying the Holy Eucharist to those who "support shopping on Sunday," but it is a very good idea in the event that Catholic or other Christian employees must work on Sunday as a condition of employment. The obvious answer to how many days are involved is to protect the right of Muslims not to work on Fridays, Jews not to work on Saturdays and any other bona fide believer not to work on similarly Holy Days. Some Catholic employers give all of their employees additional paid holidays on the Church's Holy Days of Obligation: Feast of the Circumcision, Ascension Thursday, the Feast of the Assumption, All Saint's Day, the Feast of the Immaculate Conception and Christmas. Some also add Good Friday.
Agnostics might be granted a celebration of the birthday of Question Mark, lead singer of the Mysterions. Atheists might observe Ayn Rand's birthday, if capitalist, and Marx's birthday or Kerry's, if not.