The U.S. Justice Department is filing a lawsuit challenging the constitutionality of Arizona’s tough new law targeting illegal immigrants. The planned lawsuit was confirmed to The Associated Press by a Justice Department official with knowledge of the plans. The official didn’t want to be identified before a public announcement planned for later Tuesday.

The lawsuit will argue that Arizona’s new measure requiring state and local police to question and possibly arrest illegal immigrants during the enforcement of other laws, like traffic stops, usurps federal authority