Lee gained national attention in 2001 as the only member of congress to vote against the Authorization for Use of Military Force Against Terrorists (AUMF), stating that she voted no not because she opposed military action but because she believed the AUMF, as written, granted the president overly broad powers to wage war at a time when the facts regarding the situation were not yet clear. She "warned her colleagues to be 'careful not to embark on an open-ended war with neither an exit strategy nor a focused target'".[20] Lee has said:
It was a blank check to the president to attack anyone involved in the September 11 events—anywhere, in any country, without regard to our nation's long-term foreign policy, economic and national security interests, and without time limit. In granting these overly broad powers, the Congress failed its responsibility to understand the dimensions of its declaration. I could not support such a grant of war-making authority to the president; I believe it would put more innocent lives at risk. The president has the constitutional authority to protect the nation from further attack, and he has mobilized the armed forces to do just that. The Congress should have waited for the facts to be presented and then acted with fuller knowledge of the consequences of our action.[21]
Her vote made national news and a large and extremely polarized response, with the volume of calls gridlocking the switchboard of her Capitol Hill office. Although it appears to have reflected the beliefs of the majority of her constituents, the majority of responses from elsewhere in the nation were angry and hostile, some calling her "communist" and a "traitor". Many of the responses included death threats against her or her family to the point that the Capitol Police provided round-the-clock plainclothes bodyguards.[21] Lee was also criticized by politicians and in editorial pages of conservative-leaning newspapers, e.g. John Fund's column in The Wall Street Journal.[22] In 2002, she received the Seán MacBride Peace Prize from the International Peace Bureau for her vote.