Members of the staff union Unifi and the Banking, Insurance and Finance Union will join forces to picket around 150 of Barclays' 2,000 branches.
Barclays will face calls for further talks over pay but the bank insists the settlement is "fair and competitive" and has been boosted by a profit sharing bonus of 7.5%.
Unifi said today that Barclays had backed down from its threat to sack staff involved in the strike and the union now expects most of its 40,000 members to support the action.
Most branches will be closed or will operate on a skeleton staff and those which do open will only offer "minimal services", said general secretary Paul Snowball.
He said staff had been awarded below inflation pay rises for four years in a row and although bonuses were given, they were discretionary and non-pensionable.
"The bank faces a virtual shutdown tomorrow and we are confident most of our workers will support the strike," he said tonight.
Unifi claims its 5,000 members who work as managers are pressing to be ballotted over pay and could join any future strikes.
Unifi's executive will meet on Thursday to decide its next move in the dispute.
Barclays has said it will do everything it can to ensure inconvenience to customers is kept to a minimum tomorrow.
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