26 U.S.C. § 9035

(a) Expenditure limitations No candidate shall knowingly incur qualified campaign expenses in excess of the expenditure limitation applicable under section 315(b)(1)(A) of the Federal Election Campaign Act of 1971, and no candidate shall knowingly make expenditures from his personal funds, or the personal funds of his immediate family, in connection with his campaign for nomination for election to the office of President in excess of, in the aggregate, $50,000. (b) Definition of immediate family For purposes of this section, the term “immediate family” means a candidate’s spouse, and any child, parent, grandparent, brother, half-brother, sister, or half-sister of the candidate, and the spouses of such persons.