June 23 (Reuters) - The Australian dollar fell to a session low against the U.S. dollar on Wednesday in a volatile session after Australian Prime Minister Kevin Rudd agreed to his deputy Julia Gillard's request for her to challenge for the leadership and called a vote of ruling party lawmakers.

The Australian dollar was last down 0.6 percent against the dollar at $0.8672 AUD= after going as low as $0.8662.

(Reporting by Nick Olivari, Editing by Chizu Nomiyama)