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Aparty-line vote in adeliberative assembly (such as aconstituent assembly,parliament, orlegislature) is a vote in which a substantial majority of members of apolitical party vote the same way (usually in opposition to the other political party(ies) whose members vote the opposite way).
Sources vary on what proportion of party members must adhere to theparty line in order for the vote to constitute a "party-line" vote. For example, in theUnited States, theCongressional Record has stated: "A party-line vote is one on which a majority ofRepublicans vote one way and a majority ofDemocrats vote another. 2. A bipartisan vote is one in which a majority of Republicans and a majority of Democrats vote the same way".[1] Another source defined this event for purposes of classifying votes for research purposes as "one where 90 percent of the majority party votes against 90 percent of the minority party".[2] Party-line votes are also noted to reflect the degree to which the division of power requires parties to retain cohesion in order to implement its goals:
Whether a party-line vote appears on an issue reflects incentives presented by majority rule. In a house where the two parties are nearly evenly balanced, a few defections will be very costly to the (slim) majority party, and party-line votes may prevail. If, in contrast, one party has a substantial majority, some position-taking defections can be permitted.[3]
In theU.S. Congress, it is the function of theparty whip of each party in each house to ensure that members adhere to party policies and in particular that members vote for or againstbills, amendments, and (in the case of theU.S. Senate) for or againsttreaties and administrationappointments as determined by senior party leadership. The leverage available to the party whip may be in rewards (such as the negotiation of side deals forpork barrel spending) or in punishments (such as withholding appointments to powerful committees). The ultimate threat is to support another candidate in theprimary election with endorsements and party funds. The party whip will operate under the direction of the particular party's leader (called respectively themajority leader or theminority leader).
Prior to the 1980s, it was not uncommon for members of theU.S. House of Representatives to "cross the aisle" and vote for legislation supported by the opposing party. By the mid-1990s, however, the House became almost completelypartisan andpolarized.[4]
