The union says it is prepared to take the issue to national arbitration.
The changes were proposed two years ago as part of the fire service's organisational review, with the aim of reducing the total working hours and weekend shifts.
Assistant chief fire officer Simon Smith says he does not believe the FBU is being fair.
'We also feel that in some ways the FBU is not fully representing the wishes of the members on this issue. If they dropped it, we would be delighted'.
And Leicestershire Fire Service may be sending fewer officers to attend fires because of overspending on its budget, according to BBC Leicester.
The county's deputy chief fire officer Clive Teare said the brigade has had one of its busiest ever summers, often dealing with more than 100 incidents a day. Today chief fire officer Norman Dickerson will appeal to the county council for extra cash to meet the shortfall.
Mr Teare fears serious cutbacks will have to be made if the request is refused.He said: 'The effect on the brigade would be enormous. We had a 12% increase in our workload last year; we absorbed that into the budget.
'Both in terms of operational capability and effectiveness, we would have to take a serious review of how we use our personnel - how many personnel we send to operational incidents'.