In legislative procedure, a rider is an additional provision added to a bill or other measure under the consideration by a legislature, having little connection with the subject matter of the bill. Riders are usually created as a tactic to pass a controversial provision that would not pass as its own bill. Occasionally, a controversial provision is attached to a bill not to be passed itself but to prevent the bill from being passed (in which case it is called a wrecking amendment or poison pill).
United States 
The use of riders is prevalent and customary in the Congress of the United States, as there are no legal or other limitations on their use.
Riders are most effective when attached to an important bill, such as an appropriation bill, because to veto or postpone such a bill could delay funding to governmental programs, causing serious problems.
When the veto is an all-or-nothing power as it is in the United States Constitution, the executive must either accept the riders or reject the entire bill. The practical consequence of the custom of using riders is to constrain the veto power of the executive.
To counteract riders, 43 of the 50 U.S. states have provisions in their state constitutions allowing the use of line item vetos so that the executive can veto single objectionable items within a bill, without affecting the main purpose or effectiveness of the bill. In addition, the Line Item Veto Act of 1996 was passed to allow the President of the United States to veto single objectionable items within bills passed by Congress, but the Supreme Court struck down the act as unconstitutional in Clinton v. City of New York.
Riders are often completely irrelevant to the bill they are attached and are commonly used to introduce unpopular provisions. For example, a rider to stop net neutrality was attached to a bill relating to military and veteran construction projects.
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In Canada, because of the rigid system of party control both in the federal Parliament and in provincial legislatures, the use of riders is rare. Furthermore, Canadian convention prohibits anyone other than a Minister from proposing a bill or an amendment to a bill that would require the government to spend money ("money bill").
In Canadian politics, in order to use a rider to force the passage of partisan legislation in a minority government, the proposed vote that the rider is attached to must be a confidence vote in a political atmosphere where the opposition parties are reluctant to force an election by toppling the government. One illustration of this technique is Conservative Prime Minister Stephen Harper's attachment of a rider removing public funding from Canadian political parties to a confidence vote on a Canadian economic update in late 2008.
The Constitutional Council of France has taken an increasingly hard view against riders, which it considers unconstitutional and contrary to the rules of procedure of the parliamentary assemblies. In 1985 the Council started striking down amendment to laws because they were unrelated to the subject of the law. Two special categories of riders merit mention: the "budgetary riders", attached to budget bills, and "social riders", attached to the budget bill for social security organizations,: clauses that have no link to the budget or to the social security budgets, respectively.
In some legislative systems, such as the British Parliament, riders are prevented by the existence of the long title of a bill that describes the full purpose of the bill. Any part of the bill that falls outside the scope of the long title would not be permitted. However, legislators often bypass this limitation by naming a bill vaguely, such as by appending "and for connected purposes" to the name.
In 2005, the Constitutional Court of Hungary struck down the yearly national budget law in its entirety, because almost half of the paragraphs were not related to state fiscals at all, but modified 44 other existing pieces of legislation, which concerned health regulations, public education and foreign relations. This judicial ruling restricted the government's future options in bypassing due parliamentary debate and imposing certain reforms unilaterally.
See also 
- Merriam-Webster Dictionary
- Sen. Hutchison moves to block funds for FCC on net neutrality rules
- Services of the Constitutional Council of France, État de la jurisprudence du Conseil constitutionnel sur le droit d'amendement
- Les Cahiers du Conseil constitutionnel, Cahier n° 22, Commentaire de la décision n° 2006-544 DC du 14 décembre 2006