Here you go. The Section 31 fee is not limited to $3.75 actually, but cannot be avoided regardless of your broker.

# What are SEC Section 31 fees and how are they calculated?
The normal calculation for SEC Section 31 fees is .0000257 multiplied by the principal amount on sales. A principal amount of $390 would be subject to a Section 31 fee of $.01. These fees are passed through from Zecco Trading to your accounts as a non-commission fee.

# What is the Trading Activity Fee (TAF) and why is it charged to my account?
The FINRA assesses the TAF on its members through clearing and self-clearing firms at a rate of $.000075 per share, with a maximum of $3.75 per trade on all liquidation (sell) orders. These fees are passed through from Zecco Trading to client accounts as a non-commission fee.