Ancient history, or is it, but I doubt that it is or ever was illegal or unethical or unconstitutional for the FBI to conduct surveillance of a citizen known or suspected of associating with known or suspected Communists or Communist organizations known or suspected of being Soviet sympathizers and/or fellow travellers.
Such as, for example, Rev. M. L. King, Jr. Over-reaction by the Congress, especially by the Committee chaired by Sen. Frank Church, resulted in the erection of the infamous wall between the FBI and CIA, and we know how much harm that did in relation to the Islamic terrorist attack on 9/11/2001.