During his Senate career, Fannin was a hard-line conservative, often voting with Senator Goldwater on the issues, including his vote against the Equal Rights Amendment in 1972. As the ranking Republican on the Senate Interior Committee, he was a spokesman for Presidents Richard Nixon and Gerald Ford on energy policy; he opposed new limits on strip mining and tighter reins on federal lands. He also joined conservative Democratic Senators to preserve the clause of the Taft–Hartley Act that let the states decide whether to prohibit mandatory membership for workers in unionized shops. In 1968, he became the principal sponsor behind the Central Arizona Project, which diverted water of the Colorado River to central and southern Arizona.