In a letter Monday, ACLU asked members to vote "yes" on the disapproval resolution introduced by Rep. Joaquin Castro (D-Texas) in the House last week. The measure is expected to get a vote and pass the chamber of Tuesday.

ADVERTISEMENT ACLU is one of several groups suing President Trump over the executive action he took after Congress refused to give him $5.7 billion in federal funding to build a wall along the southern border.

The spending bill Congress passed, and that the president ultimately signed, only allotted $1.375 billion to build border barriers.

Under the emergency declaration, Trump plans to pull $3.6. billion from military construction projects, $2.5 billion in funding the Defense Department uses to support counter-drug activities in states and $601 million from the Treasury Forfeiture Fund, which is used to support state law enforcement programs.

ACLU argues the emergency declaration undermines the Constitution and violates federal funding laws, and the group says Congress has to act in addition to the courts.

"While the ACLU, other organizations, and numerous states have petitioned federal courts to defend the Constitution against the unlawful declaration of a non-existent emergency, H.J. Res. 46 is an opportunity for Congress to assert its own role in defending the Constitution," Ronald Newman and Christopher Anders, the group's national politics director and deputy director, said in the letter.

"You and your colleagues have the same sworn, solemn obligation that the President and every federal judge has to uphold and defend the Constitution."