The taxpayer-backed group will axe 210 posts by closing a customer service unit in Kent, with another 320 jobs to go from retail banking operations elsewhere in the UK, including operations in London and Birmingham.
In April, the bank said it planned to reduce its workforce by 985 staff over the next two years as it consolidates its operations in the wake of the merger.
That number now looks like being exceeded, as LBG had already announced 625 job losses last month.
Ged Nichols, general secretary of union Accord, said taxpayers would expect LBG to work in partnership with employee representatives to ensure "unnecessary unemployment" and compulsory redundancies are avoided, "particularly given the support UK taxpayers have provided to the bank".
The Treasury owns 43.4 percent of LBG following its emergency bailout of the bank.