Activist group GetUp! will target penalty fees in a new campaign aimed at recovering money consumers have lost to banks.

GetUp! will encourage its 375,000 members to contact the heads of Australia's largest banks to warn them they will move their business elsewhere if banks don't reduce penalty fees and refund amounts paid.

The group is also prompting its members to join the class action suit being funded by IMF to recover "illegal penalties charged by banks".

"Initially we will focus on penalty fees which we do think need a better resolution than what the banks have so far offered," GetUp! national director Simon Sheikh said.

"There are a number of penalty fees on credit cards that some of the big banks are still charging," he said.