The American Civil Liberties Union said Friday it will challenge the Trump administration's latest travel ban, the first such legal action to be announced against the new ban.

The ACLU and other groups who had previously sued over the administration's ban on visitors from six majority-Muslim countries said in a letter Friday to a federal judge in Maryland that they want to amend their existing lawsuit. The groups say the latest version of the ban, the administration's third, also violates federal law and the Constitution.

Trump announced the latest restrictions last weekend after the previous ban expired. The restrictions are targeted at countries that the Department of Homeland Security says fail to share sufficient information with the U.S. or haven't taken necessary security precautions. The new restrictions impact citizens of Chad, Iran, Libya, North Korea, Somalia, Syria, and Yemen — and some Venezuelan government officials and their families — and are to go into effect Oct. 18. The prior ban also included Sudan but didn't include Chad, North Korea or Venezuela.

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In their two-page letter, the ACLU and others say they want to amend their existing lawsuit to cover the president's latest proclamation and seek a preliminary injunction "or other relief" suspending the visa and entry restrictions in the proclamation.

Justice Department spokesman Ian Prior told the Associated Press in an email after the ACLU announced its intention to take legal action that the department "will continue to vigorously defend the President's inherent authority to keep this country safe."

The travel ban continues to be a point of controversy for the Trump administration, although the issue has been overshadowed by a number of other issues since it first became a problem for the Trump administration at the beginning of his presidency.

The process for developing this travel ban was more rigorous than the two previous bans. The Department of Homeland Security worked with the State Department to issue standards for vetting individual travelers that each nation needed to meet, and gave all countries 50 days to reach those requirements. Then, Acting DHS Secretary Elaine Duke gave those recommendations to the president, and Mr. Trump had a week to consider the countries that met and failed to meet those standards. Administration officials had hoped this ban would be more difficult to challenge in court.

This ban, unlike the previous bans, has no expiration date. Rather, it's a conditions-based ban, and countries with restrictions will remain restricted until they fulfill the standards set by the Trump administration.