Washington (CNN) Four members of the Homeland Security Advisory Council, which advises the Department of Homeland Security, have resigned, saying in a letter that they can no longer be associated with the Trump administration's immigration policies and calling the separation of migrant families "morally repugnant."

The letter, which was obtained by CNN, was addressed to Homeland Security Secretary Kirstjen Nielsen and signed by Richard Danzig, David Martin and Matthew Olsen -- all former Democratic administration officials -- and by Elizabeth Holtzman, a former Democratic congresswoman from New York.

The four said in the letter that "unfortunately," they had not been consulted "before recent immigration decisions were announced, enforced, and then retracted by this administration" and that had they been consulted, they would have "observed" that family separations were not only morally repugnant, but also "counter-productive and ill-considered."

Last month, President Donald Trump abruptly reversed course after facing a backlash over the separation of undocumented families at the border and signed an executive order to halt it. The US government has since been ordered by a federal judge to reunite separated families, a process that is ongoing. CNN has previously reported that the government hasn't been able to locate the parents of 71 children who were likely separated from them.

The resignations were first reported by The Washington Post.

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