Catholics are bound to follow canon law when getting married. For a Catholic to be validly married he or she must be married in the Church (Canon 1108) or if a Catholic is marrying a nonCatholic he or she may receive permission from their Bishop to be married in another church or setting (Canon 1118).
Thus if a Catholic is civilly married without permission from their Bishop then they are in an invalid marriage and cannot receive communion until they have their marriage validated by the Church.
