The phrase "to affect those banks" means to have an impact or influence on the banks. It suggests that something is having an effect on the banks, possibly in a negative or significant way. Full definition
I'm personally convinced that the next crisis is going to affect the banking system heavily. (claudiograss.ch)
You can expect the short sale to significantly and negatively affect a bank's interest in lending you money. (rismedia.com)
You don't know when the worst will happen, and you don't want to be on the fence about taking action because of how it'll affect your bank account. (policygenius.com)