The Taoiseach says he expects to see the people who were wrongly taken off tracker mortgages compensated by the banks before Christmas.
Leo Varadkar was speaking ahead of Finance Minister Paschal Donohoe meetings with top bankers on Monday and Wednesday.
Thousands of customers of several Irish lenders were overcharged or wrongly denied a tracker rate.
The Central Bank says at least 13,000 accounts were impacted, but it's believed that up to 30,000 people may have been affected.
Compensation has been paid to around 3,300 affected customers - with Leo Varadkar saying it's 'not good enough' that less than half of people have been compensated.
The Taoiseach says new taxes could be put on the banks if they don't make things right.
He suggested: "We're very frustrated at the lack of progress to date - and we're certainly not ruling out further regulations, further sanctions or additional taxation on the banks as the case may be."