A blank check (carte blanche) is a check that has no numerical value written in, but is still signed. (Check owners are normally advised to specify the amount before signing.) If created accidentially, such checks can be extremely dangerous for their owner, for whoever obtains the check could write in whatever amount of money he wanted, and would legally be able to cash it.

The metaphor of the "blank check" is thus often used in politics to describe legislation that is open-ended or vague, and could be easily subjected to abuse. For example, in the US the Gulf of Tonkin Resolution has been called a "blank check," for it gave the President the power to "to take all necessary measures" to prevent "aggression" in Southeast Asia. These powers were then used to escalate the Vietnam War. Many in the Congress protested, but were helpless to do so, for the Tonkin resolution's terms were too subjective to enforce.

see also: list of political metaphors