June 28th, 2020
President Lyndon B. Johnson approved PL 90–363, which amended section 6103(a) of Title 5, United States Code, establishing Monday observance of Washington’s Birthday, Memorial Day, Labor Day, Columbus Day and Veterans Day. The new holiday law took effect Jan 1, 1971. Veterans Day observance subsequently reverted to its former observance date, Nov 11.
Source: www.presidency.ucsb.edu/ws/?pid=28963