The civil rights group said Friday that it was seeking to amend an existing lawsuit that was filed in a Maryland federal court, challenging a previous Trump immigration order.
The ACLU said it was seeking an injunction to block visa and entry restrictions on those affected by the order, saying the ban violates the U.S. Constitution and U.S. immigration law.
Trump announced the revised travel order on Sunday as a previous temporary ban on visitors from six Muslim-majority countries expired.
The new restrictions affect citizens of Chad, Iran, Libya, North Korea, Somalia, Syria, Venezuela and Yemen.
U.S. officials say these countries have refused to share information about terrorism and other issues with the United States.
The earlier immigration order had barred citizens of Iran, Libya, Somalia, Sudan, Syria and Yemen from entering the United States unless they had a “credible claim of a bona fide relationship with a person or entity in the United States.”
That earlier order was blocked by lower courts in the United States, but it was partially held up by the U.S. Supreme Court.
Trump said in the new proclamation: “As president, I must act to protect the security and interests of the United States and its people. The restrictions announced are tough and tailored, and they send a message to foreign governments that they must work with us to enhance security.”
Challengers of the immigration restrictions argue that they are aimed at blocking Muslims from entering the United States.
The revised travel order goes into effect October 18.