The US Coast Guard has now made it mandatory to wear the kill switch cord when above idle speed. This applies to any boat with 3 hp or more, and boats less than 26 ft in length.

Older boats that do not have a kill switch cord are exempt. If a kill switch system is in place, it must be utilized and the cord attached to the boat operator.

The new law goes into effect on April 1st.

U.S. Coast Guard Announces New Law Requiring Use of Engine Cut-off Switches | National Safe Boating Council