Suncorp Bank has withdrawn its service guarantee after its low variable rate prompted a "substantial increase" in volumes.
The bank announced on October 3 that it had temporarily reduced its Home Package Plus discounted rate to 4.69 per cent, with the offer valid until December 12.
Suncorp said the "overwhelming" response from brokers had placed pressure on its back end.
"Given the substantial increase in the volume of lodgements we have seen, we are experiencing pressure on turnaround times," the bank said in a statement.
"As such, Suncorp Bank has made the decision to withdraw its service guarantee until further notice."
Suncorp told brokers on Friday that it wanted to be transparent with them so they could manage the expectations of their customers.
"We're proud of the success of our service guarantee over the past 15 months, with service delivery being pivotal to our overall proposition to our brokers and customers," the letter said.
"We would like to reinforce that during this peak time, service turnarounds remain a key priority for us.
"Our operations and broader areas of the bank are all hands on deck to ensure that our time lines remain as close to six days to first decision as possible during what we are expecting to be two very busy weeks as the campaign closes off on December 12."
The letter also said that Suncorp would provide daily updates about current turnaround times on its broker website.