President Trump faces legal challenges to his decision to use emergency powers to build a wall on the US border with Mexico.
California and New York said they would take legal action to challenge his move to bypass Congress and secure funding for the project.
Building the wall was a key pledge of Mr Trump’s campaign.
Democrats said it was a “gross abuse of power” and vowed to contest it “using every remedy available”.
On Friday, Mr Trump signed the emergency declaration along with a spending bill aimed at preventing a repeat of a recent government shutdown.
Declaring an emergency could give him access to billions of dollars. Mr Trump announced the plan after Congress refused funding for the wall.
Within hours, the first legal challenge against the declaration of national emergency was launched.
A liberal advocacy group, Public Citizen, sued on behalf of a nature reserve and three Texas landowners who have been told the wall may be constructed on their properties.