Members of the finance union Unifi voted overwhelmingly for action following the decision.

The bank opted to remove some staff from its final salary pension scheme after deciding to transfer the staff to its outsourced computer specialist SCC.

From 12 May an overtime ban will begin, which may escalate if the Co-op Bank maintains its stance, Unifi warned.

Unifi officer Andy Colognori said: "Essentially the Co-op Bank is going to make money out of dumping staff from its pension scheme so it will no longer have to provide contributions to the fund."

The union warned that it may consider strike action "if there is no movement" from the bank.