In legislative debate, a wrecking amendment (also called a poison pill amendment or killer amendment) is an amendment made by a legislator who disagrees with the principles of a bill and who seeks to make it useless (by moving amendments to either make the bill malformed and nonsensical, or to severely change its intent) rather than directly opposing the bill by simply voting against it.
An important character of wrecking amendments is that they are not moved in good faith. The proposer of the amendment would not see the wrecked legislation as good legislation and would still not vote in favour of the legislation when it came to the final vote, even if the amendment were accepted. Motives for making them include allowing more debate, delaying the enactment of the legislation, or just sometimes a straightforward attempt to make the initiator of the legislation give up.
Some opponents of particular amendments will describe them as wrecking amendments because they regard the amendments as undermining the unity of the original proposal. Proponents of the amendment may seek to deny the charge by saying that the original proposal brings together different steps, and while personally they oppose all the parts, some parts are even worse than others and legislators should have an opportunity to consider them separately.
Wrecking amendments can pick up more votes than motions against, because observers tend to focus on who voted in favour and against the Bill in the final count, rather than looking at the amendments made during the passage through the legislature. Therefore it can be a wise tactic to try to introduce wrecking amendments at as many opportunities as possible.
Recent examples of wrecking amendments include the United Kingdom's Gender Recognition Act 2004, which was brought forward to enable legal recognition of the new gender of transsexual people and included a specific provision to allow transsexual people to marry. In the House of Lords, Norman Tebbit moved an unsuccessful amendment to leave other provisions of the Bill intact but forbid such marriages.