In the Eastern Orthodox Churches, in order to be considered a "member" of the Church capable of voting on important issues in your local church, or serving on the church council, etc., you are obligated to give a specific amount of money delegated by your local diocese. This is to be given in addition to tithing or any other offering.
Does the Coptic Orthodox Church also assign "dues" to its members in order to accept them as members of the Church?
To be a member of the Orthodox Church, we need to ask ourselves: Who is the Church? The Church is a group of people who believe in their communion with God the Father, in Jesus Christ the incarnate Word of God, by His Holy Spirit. This is how we conceive of redemption, membership in the church, a deep understanding of the Holy Bible, an acceptance of the Kingdom of God within our souls, a communion with the saints and the angels, and the experience of eternal life.
In the Old Testament, the children of Abraham had the covenant of circumcision with God (Gen 17). In the New Testament Christ offered a new covenant, His Body and Blood, on the cross presenting them as the Eucharist to His people, the Church.
To be a member in the Orthodox Church, you have to be baptized, and partake in the Holy Mysteries of the Church. Any faithful member can serve in the Church.
The Coptic Orthodox Church doesn't ask anyone for specific dues. Members give their tithes and their donations to Church willingly not only because it is mentioned in the Holy Bible, but because of all the blessings that come with it. You can read more about this in the article titled, "The Virtue of Giving": http://www.suscopts.org/literature/literature.php?misc=search&subaction=showfull&id=1102863028&archive=&cnshow=news&start_from=&.