Northern Rock has plans to cut up to 650 jobs during the remainder of 2010.
The move forms part of a restructuring programme aimed at preparing the nationalised lender for a sale.
A consultation has begun with trade union, Unite, and compulsory redundancies will be avoided where possible.
However, Unite claims the number of jobs cut will be 990, on top of the 2,000 already lost since 2008, the BBC has reported.
Explaining the move, the Rock’s chief executive, Gary Hoffman, says: “In order to meet our objectives, we must align our staffing level to match the smaller size of the business.”
Last week, the bank announced that it is closing its operations in Guernsey in preparation for its return to private ownership.
Around 6,000 customers of Northern Rock (Guernsey) Limited have been notified and advised of the process required to close their accounts in full.