South Yorkshire Police has revealed a special protest unit has been set up for the Liberal Democrat conference in Sheffield next month.
About 1,000 officers will be on duty for the three-day conference, which starts on 11 March, in an operation expected to cost about £2m.
The cost, borne by the police, comes as the force tries to make £15m of savings.
The party cancelled a London conference in December due to protest threats.
'Strength of feelings'
Officers' leave has been cancelled so the force can mount a 24-hour security operation for the duration of the event, as well as carry out normal duties.
Supt Martin Scothern said contingency plans were in place in case of "excessive behaviour".
He added: "There needs to be an operation put together that can deal with all eventualities.
"London is a different place, but I'm aware of some of the strength of feelings.
"We are expecting some protests and we're talking to some protest groups and for that purpose we have set up a dedicated protest liaison team for people whose intentions are to peacefully protest."
Labour Councillor Shaun Wright, from the police authority, said it was "ironic" the force would have to pay for the service for the political party who had a hand in devising its cuts.
It is thought to be the biggest operation staged by South Yorkshire police since the G8 summit in 2005.