Airline passengers will be able to carry small knives, golf clubs and souvenir baseball bats onto US planes from next month.
The new policy, announced by the head of the US Transportation Security Administration (TSA), is intended to conform with international standards.
The TSA said it will allow it to focus its energies on more serious safety threats, but the reform angered unions representing airline workers.
David Castelveter of the TSA said the policy change came after an internal working group decided the items represented no real danger.
He said the presence on flights of gun-carrying pilots travelling as passengers, federal air marshals and airline crew members trained in self-defence provide additional layers of security to protect against misuse of the items.
The new policy permits folding knives with blades that are 2.36 inches or less in length and are less than 1/2-inch wide. It is aimed at allowing passengers to carry penknives, corkscrews with small blades and other knives.
Passengers will also be allowed to bring onboard as part of their carry-on luggage novelty-sized baseball bats less than 24 inches long, toy plastic bats, billiard cues, ski poles, hockey sticks, lacrosse sticks and two golf clubs. The policy goes into effect on April 25.
Box cutters, razor blades and knives that do not fold or that have moulded grip handles will still be prohibited, the TSA said.
Transport Workers Union Local 556, which represents more than 10,000 flight attendants at Southwest Airlines, called the new policy "dangerous" and "short-sighted," saying it was designed to make "the lives of TSA staff easier, but not make flights safer".
The union said: "While we agree that a passenger wielding a small knife or swinging a golf club or hockey stick poses less of a threat to the pilot locked in the cockpit, these are real threats to passengers and flight attendants in the passenger cabin."