All votes for Representatives in Congress must be by written or printed ballot, or voting machine the use of which has been duly authorized by the State law; and all votes received or recorded contrary to this section shall be of no effect.
Structure US Code
CHAPTER 1— ELECTION OF SENATORS AND REPRESENTATIVES
§ 1. Time for election of Senators
§ 1a. Election to be certified by governor
§ 1b. Countersignature of certificate of election
§ 2b. Number of Representatives from each State in 78th and subsequent Congresses
§ 2c. Number of Congressional Districts; number of Representatives from each District
§ 5. Nominations for Representatives at large