While there were some groups and individuals that were opposed to the United States being involved in any war, there was no official group that was created solely to oppose the United States being involved in World War I.
People who were against our involvement in World War I would have been against our involvement in any war. Some of these people were progressive reformers such as Jane Addams and business owners such as Andrew Carnegie. During the war, more radical groups opposed our involvement in World War I. These included Marxists and anarchists. There were religious groups that also weren’t in favor of us joining the war. Some individuals did protest the war by not serving in the war when they were drafted.
German-Americans were concerned about the United States joining World War I. These people were concerned they would experience discrimination and poor treatment by the American people.
Overall, there was no major group that was created only to denounce our involvement in World War I. While there were some groups and individuals against our involvement in the war, there was no formal, organized opposition to our involvement in World War I.