Pay talks for WestpacTrust's IT staff are due to begin later this month.
The Finsec union has a "pretty small" number of staff among it's 2500 WestpacTrust members, says general secretary Don Farr.
Those numbers have been diminished in recent years as a "big chunk" of banking IT staff have shifted to companies such as IBM and EDS following IT outsourcing deals, says Farr.
The current disruptions affect mainly customer service staff, since Finsec's remaining IT staff are covered by another agreement. But the "process or bargaining" for them will begin in several weeks, Farr says.
Electronic and telephone transactions remain unaffected.