The donor determines if a contribution is unrestricted or restricted. Most of the Sunday offering is unrestricted since the donor has not specified how it should be used. These contributions can be used to pay for the normal operating expenses of the church.
When the church asks for donations to a specific project, however, donations to that project are temporarily restricted; they must be spent for a specific purpose. A permanent restriction generally indicates that the church is limited in its use of the donation, frequently to spending the income earned on a donation for a specified purpose. It is important to remember that only the donor (or heirs) can remove a restriction from a specific gift.
More information can be found in the Finance Guidelines published by Cokesbury each quadrennium.