Standard Time Act

The Standard Time Act of 1918, also known as the Calder Act, was the first United States federal law implementing Standard time and Daylight saving time in the United States. It authorized the Interstate Commerce Commission to define each time zone.

The section concerning daylight saving time was repealed by the act titled An Act For the repeal of the daylight-saving law, Pub.L. 66–40, 41 Stat. 280, enacted August 20, 1919, over President Woodrow Wilson's veto.

Section 264 of the act mistakenly placed most of the state of Idaho (south of Salmon River (Idaho)) in UTC−06:00 CST Central Standard Time, but was amended in 2007 by Congress to UTC−07:00 MST Mountain Standard Time. MST was observed prior to the correction.