The US said on Thursday it would try to persuade all air passengers to shuffle through airport security checks in their socks.
The authorities were "clarifying" their anti-shoe-bomb policy to help speed up clearance procedures, said a Transport Security Administration (TSA) statement.
Passengers would be "encouraged" but not required to remove their shoes and submit them for X-ray examination before going through metal detectors, TSA administrator James Loy said.
People who kept their shoes on would have a bigger risk of being selected for a more thorough, secondary screening. Thick-soled shoes and those with metal shanks or steel toes, in particular, would be targeted.
The latest policy was part of a drive for consistency.
"Our screeners have always worked hard to make sure a `shoe bomb' does not get on an aircraft," Loy said.
"Now we must make sure our security process is consistent so air travelers know what to expect at every airport in the country," he said.