26 USC 276 - Certain indirect contributions to political parties

(a) Disallowance of deduction 
No deduction otherwise allowable under this chapter shall be allowed for any amount paid or incurred for
(1) advertising in a convention program of a political party, or in any other publication if any part of the proceeds of such publication directly or indirectly inures (or is intended to inure) to or for the use of a political party or a political candidate,
(2) admission to any dinner or program, if any part of the proceeds of such dinner or program directly or indirectly inures (or is intended to inure) to or for the use of a political party or a political candidate, or
(3) admission to an inaugural ball, inaugural gala, inaugural parade, or inaugural concert, or to any similar event which is identified with a political party or a political candidate.
(b) Definitions 
For purposes of this section
(1) Political party 
The term political party means
(A) a political party;
(B) a National, State, or local committee of a political party; or
(C) a committee, association, or organization, whether incorporated or not, which directly or indirectly accepts contributions (as defined in section 271 (b)(2)) or make expenditures (as defined in section 271 (b)(3)) for the purpose of influencing or attempting to influence the selection, nomination, or election of any individual to any Federal, State, or local elective public office, or the election of presidential and vice-presidential electors, whether or not such individual or electors are selected, nominated, or elected.
(2) Proceeds inuring to or for the use of political candidates 
Proceeds shall be treated as inuring to or for the use of a political candidate only if
(A) such proceeds may be used directly or indirectly for the purpose of furthering his candidacy for selection, nomination, or election to any elective public office, and
(B) such proceeds are not received by such candidate in the ordinary course of a trade or business (other than the trade or business of holding elective public office).
(c) Cross reference 
For disallowance of certain entertainment, etc., expenses, see section 274.