Three-Line Whip

A three-line whip is the most binding form of voting instruction used in Westminster-style parliaments, named for the practice of underlining the relevant item three times in the weekly written notice ("the whip") sent by party whips to their MPs. A one-line whip is merely an advisory note; a two-line whip requires attendance unless paired with an absent opponent; a three-line whip demands both presence and a vote in accordance with the party's position.

The mechanism is central to party discipline in the United Kingdom House of Commons and is also used in the parliaments of Canada, Australia, India, Ireland, and other Commonwealth legislatures. In the UK, defying a three-line whip can result in the MP having the whip "withdrawn," meaning they sit as an independent until readmitted. A high-profile instance occurred in September 2019, when Prime Minister Boris Johnson removed the Conservative whip from 21 MPs—including former chancellors Philip Hammond and Kenneth Clarke—who voted against the government on a Brexit-related motion to take control of the order paper.

In India, the three-line whip carries additional legal weight: under the Tenth Schedule of the Constitution (the anti-defection law, added by the 52nd Amendment in 1985), a legislator who votes against a party whip can be disqualified from the legislature by the Speaker, subject to certain exceptions for splits and mergers. This makes Indian three-line whips substantially more coercive than their British counterparts, where consequences remain political rather than constitutional.

Whips are typically issued for confidence votes, budget legislation, and contested government bills. Free votes—matters of conscience such as capital punishment or some social legislation—are explicitly not whipped. The system relies on the office of the Chief Whip, who manages party attendance, communicates leadership expectations, and negotiates "pairing" arrangements with counterparts in opposing parties.