To ensure tax deductibility of contributions to the church, the church needs to issue acknowledgement in writing of the contributions and contributors should not file their 2013 tax returns until they have received that acknowledgement.
ManagingYourChurch.com (part of Christianity Today) suggests the following notification in newsletters and/or bulletins:
IMPORTANT NOTICE: To ensure the deductibility of your church contributions, do not file your 2013 income tax return until you have received a written acknowledgment of your contributions from the church. Some of your contributions may not be tax-deductible if you file your tax return before receiving a written acknowledgement of your contributions from the church.
Click here to see the full article from ManagingYourChurch.com.