Commonwealth Bank (ASX: CBA) branches opening on 1 August can only be staffed by employees who volunteer to work on the Bank Holiday, and those bankers must be paid penalty rates due to trading hours permit restrictions won by the Finance Sector Union.

The union’s announcement comes after Commbank said on Wednesday it will open some branches in NSW and the ACT on August 1. The bank said its application to trade on the bank holiday was approved by the NSW state government.

Union members opposed the CBA's plans to overturn the 100 year old Bank Holiday, and in the process won restrictions on trading permits that protect both staff and community interests.

“CBA branches haven't opened in New South Wales and ACT on the first Monday in August for a hundred years and many CBA workers are wondering 'why start now'?” said FSU NSW/ACT Secretary Geoff Derrick.

"Management have said it's about customer service, but if they really cared about service they would have adequate staff numbers in branches every day," he said.

The restrictions mean that any CBA retail bank branches opening on 1st August can only be staffed by employees who volunteer to work and those people will need to be paid penalty rates. Workers can't be directed to turn up to work on that day. This restriction is critical given the large number of CBA staff on individual contracts who have no control over their rosters and no penalty rates.