Airlines will be required to give flight attendants at least 10 hours off duty between shifts, up from nine, under a rule announced on Tuesday by the US Federal Aviation Administration.
Acting FAA administrator Billy Nolen said that the extra hour of rest would contribute to safety.
The rule goes into effect in 30 days, and airlines have up to 90 days to comply.
US Congress directed the FAA in 2018 to increase the rest requirement for flight attendants and eliminate a provision that let crews work with less rest under some circumstances.
“It took us way too long but we are finally here,” Mr Nolen said at Ronald Reagan Washington National Airport in Arlington, Virginia, where he was flanked by more than a dozen flight attendants.
Current federal rules allow flight attendants to work up to 14 hours in a day and get nine hours of rest between shifts.
The Association of Flight Attendants has fought for years for a longer break between shifts.
The union’s president, Sara Nelson, appeared with Mr Nolen at the airport and accused the administration of former president Donald Trump of trying to kill the increase through regulatory delays.
Union officials have highlighted a 2020-2021 increase in incidents involving unruly passengers as showing the need to give cabin crews more rest between shifts.
Airlines have reported fewer incidents since the federal requirement to wear face masks on flights ended in April.
“This is a small handful of people making it hell for flight attendants on the front lines,” Ms Nelson said.
The FAA took public comments on the extra rest requirement in 2019 and 2021, and received more than 1,000 contributions from airlines, flight attendants and the public.
Airlines for America, a trade group representing the largest US airlines, said safety was always the industry’s top priority.
“Having rested and alert flight attendants who are prepared to carry out their responsibilities, including cabin safety and other duties, is critical to this goal,” it said.
The group said it supported “scientifically validated and data-driven countermeasures to prevent fatigue".