According to the IRS:
"A charitable organization must provide a written disclosure statement to donors of a quid pro quo contribution in excess of $75. A quid pro quo contribution is a payment made to a charity by a donor partly as a contribution and partly for goods or services provided to the donor by the charity. For example, if a donor gives a charity $100 and receives a concert ticket valued at $40, the donor has made a quid pro quo contribution. In this example, the charitable contribution portion of the payment is $60. Even though the part of the payment available for deduction does not exceed $75, a disclosure statement must be filed because the donor's payment (quid pro quo contribution) exceeds $75. The required written disclosure statement must:
1. Inform the donor that the amount of the contribution that is deductible for federal income tax purposes is limited to the excess of any money (and the value of any property other than money) contributed by the donor over the value of goods or services provided by the charity, and
2. Provide the donor with a good faith estimate of the value of the goods or services that the donor received."
See Substantiating Charitable Contributions from http://www.irs.gov/Charities-&-Non-Profits/Substantiating-Charitable-Contributions for more information.