UNIT RULE. The unit rule, a practice formerly observed by the Democratic Party at its national conventions, required that the entire vote of a state delegation be cast as a unit for the candidate preferred by a majority of that delegation. The 1968 Democratic convention voted to release all delegates from the unit-rule constraint, and reforms adopted before the 1972 convention outlawed the unit rule at all stages of delegation selection. The survival of the unit rule until 1968 was largely a concession to the often dissident southern delegations in the party.
David, Paul T., Ralph M. Goldman, and Richard C. Bain. The Politics of National Party Conventions. Lanham, Md.: University Press of America, 1984.
Parris, Judith H. The Convention Problem: Issues in Reform of Presidential Nominating Procedures. Washington, D.C.: Brookings Institution, 1972.