HR staff at Lloyds TSB and HBOS face the axe after initial details of the £12.2bn takeover were revealed.
According to the deal agreement, Lloyds TSB has estimated cost savings in excess of £1bn by combining the networks and back offices of the two banks.
Under the cost-saving plan retail branches will be cut, products and services rationalised and operations offshored.
Head office posts in HR, risk management, finance and legal departments are almost certain to face cuts.
The company has also refused to rule out compulsory redundancies as it looks to drastically reduce headcount. Lloyds employs 70,000 people and HBOS has 72,000 staff.
Graham Goddard, deputy general secretary of trade union Unite, said: “With an economic downturn biting, thousands of staff at both banks will be very worried about the consequences of a merger. Unite is calling for urgent talks at the highest level with the banks. We will not accept any compulsory redundancies as a result of this merger.”