The Finance Sector Union on Friday lodged a statement of claim against the Commonwealth Bank in the Federal Court, alleging that employees had not been allowed to take 10-minute rest breaks due to understaffing.

FSU national secretary Julia Angrisano estimated the claim was worth at least $45 million.

"This is a claim about rest breaks but the real issue here is that every CBA branch is so short staffed, everyone is run off their feet," Ms Angrisano said in a statement.

"We don't just want the money repaid, we want CBA to staff their branches realistically so that our members can take the breaks they're entitled to, book the leave they want, and have a sick day without being hassled to come in."

CBA workers are entitled to two paid 10-minute tea breaks - on top of their lunch break - for shifts longer than five hours, according to the statement of claim seen by AAP.

''We have not received the claim referred to in the FSU's press release," a CBA spokesperson said.

"We will carefully review it once it is served.''

Australian Associated Press