Rubber bullets could be used in cases of "extreme" disorder at a tuition-fees protest in London on Wednesday, a Scotland Yard commander has said.
About 4,000 police officers, some from other forces, will be deployed on the route, said Commander Simon Pountain.
Criminal behaviour would be dealt with "decisively and swiftly", he added.
But Jenny Jones, the Green Party mayoral candidate in London, said the idea of unarmed demonstrators being shot at was "frankly appalling".
Protesters are due to gather near the University College London campus in Bloomsbury, before heading to Trafalgar Square and Holborn, and ending near the Barbican.
Last year saw a series of similar rallies against increased tuition fees in England and changes to education allowances.
But the events in London turned violent, with an invasion of an office block on Millbank, damage to shops in Oxford Street and an attack on a limousine carrying the Prince of Wales and Duchess of Cornwall.
Permission 'takes time'
"We know the overwhelming majority of students are law-abiding and we hope this will be a peaceful event," said Mr Pountain, who is in charge of policing the march.
"We certainly don't see it as inevitable that we will witness a repeat of last year's scenes of violence and criminal damage.
"However, it would be negligent if we did not plan a response to the small minority who may be intent on disruption and may not intend to be peaceful."
In a statement, Scotland Yard said rubber bullets - also known as baton rounds - were "carried by a small number of trained officers", none of whom would be patrolling the route of the march.
"This tactic requires pre-authority, and would take time to deploy, and is one of a range of tactics we have had available for public order, and not used, in the past."
But Ms Jones, who is also a member of the Metropolitan Police Authority watchdog, said: "Any officer that shoots a student with a baton round will have to answer to the whole of London."
She said: "The prospect of the police shooting at unarmed demonstrators with any kind of bullet is frankly appalling, un-British and reminiscent of scenes currently being used by murderous dictatorships in the Middle East."