Highland Council senior management have warned councillors of a "significant worsening" in the local authority's projected financial position.
In an email, councillors have been told the council's budget gap was estimated to increase from £13.2m to £46.2m over the next three years.
Key reasons include assumptions of a cut in grant funding and changes to pensions and National Insurance.
Councillors will be asked to discuss the situation at a meeting next week.
Senior officers said there will have to be reductions in services and staffing levels.
