Young people who play their music out loud on buses in London could be stripped of their free travel passes, the mayor has said.
Ken Livingstone's announcement is part of a crackdown on anti-social behaviour and crime on buses in the city.
He called for an "absolute" ban on anyone playing music on mobile systems.
However, the Transport and General Workers' Union (T&G), said its 4,500 bus drivers are not prepared to enforce any clampdown.
Perception of safety
Speaking before the London Assembly last week, Mr Livingstone said in response to these concerns Transport for London (TfL) was adapting an upcoming campaign "to incorporate the playing of music on buses".
The campaign by TfL is designed to reduce anti-social behaviour and crime and improve "passenger perception of safety on the bus network".
Calling for an "absolute prohibition on playing music from a mobile system" Mr Livingstone said "people will be asked to leave the bus and in the case of a child with free travel concession they would forfeit it".
Jim Buckley, of the T&G, said union members had discussed the issue last week and were concerned about the enforcement aspect.
"It would mean the driver having to get out of his cab, thereby putting himself in a situation of potential assault," he told the BBC News website.
"On that basis, we don't want anything to do with it."
In September an online petition was set up by Tom Wright and girlfriend Valeria Martinelli, from Leyton, east London, which has already attracted thousands of signatures.
On Thursday Conservative MP for Castle Point in Essex, Bob Spink put forward a motion pushing for tough measures to deter bad behaviour on buses.
Those who use headphones in listening to their music will not affected by the move.
Mr Spink's motion acknowledged the need to increase passengers on London's buses but condemned fare-dodgers and those who are violent towards drivers and other passengers.
He called for "tough measures to deter, and...deal with nuisance and bad behaviour in order to maintain an effective, safe and agreeable service for all who make use of it".