While most people supported Executive Order 9066 some people were against it.FBI Director J. Edgar Hoover was one of the people against the internment camps. He was not against it though because he thought it was unconstitutional, but because he believed that most spies from the Japanese had already been arrested by the FBI shortly after the Japanese surprise attack on Pear Harbor.

You might find it surprising but the First Lady Eleanor Roosevelt was also against Executive Order 9066. She spoke privately many times with her husband. She was unsuccessful in convincing him not to sig
J. Edgar Hoover one of the few people against Japanese Internment camps
n Executive Order 9066.
First Lady Eleanor Roosevelt was also against Executive Order 9066

There were also some court cases against the internment camps.

One of the court cases was one by Endo, in 1943;

Mitsuye Endo was a nisei who had been working as a stenographer at the Department of Motor Vehicles in Sacramento, which is the capital of California. After the attack on Pearl Harbor and the relocation process, she was forced to move into an internment camp by the government in Utah with her family. Like the other one hundred thousand Japanese Americans who were removed from their homes, Endo was confused because she was not the one who bombed Pearl Harbo and she did not commit any crimes. Endo hired a lawyer, James Purcell, to represent her legal protest against her illegal relocation. Purcell and Endo filed a habeas corpus in court as a representation of her plea. The writ requested that Endo be released from the relocation camp so that she could challenge the terms of her dismissal. However, the court agreed to releasing Endo outside the West Coast area only. The U.S. government responded by offering to release Endo outside the West Coast rather than test the constitutionality of detention. Endo refused the offer and remained confined without charge for another two years as she pursued her case.

It was two years later when the U.S. Supreme Court finally said that persons of Japanese descent could not be held in confinement without proof of their disloyalty, stating that, "Detention in Relocation Centers of persons of Japanese ancestry regardless of loyalty is not only unauthorized by the Congress or the Executive, but it is another example of the unconstitutional resort to racism in the entire evacuation program."