A collateral attack, also called an indirect attack, is a challenge on the validity of a prior judgment through a new case rather than by a direct appeal. Examples include habeas corpus petitions and claims that a prior judgment was invalid after the opposing party cites it for strategic advantage in a new case.
Under the principles of res judicata, an issue/claim which has already been litigated on the merits is a bar on future lawsuits, the party is collaterally estopped from raising it again. As a result, a party wishing to re-litigate an issue/claim which has already been decided on the merits must show that the initial judgment was invalid by way of a collateral attack.
Common grounds for a collateral attack include a lack of personal jurisdiction, a lack of subject matter jurisdiction, and a failure of due process in the first case. For a collateral attack, the failure of due process is generally an inability for the party being barred to argue their side in court.
For a habeas corpus case, see Miller-El v. Dretke 545 U.S. 231 (2005).
[Last updated in July of 2022 by the Wex Definitions Team]