You can charge anyone any amount you want as long as they know about it when the deal is made.
As carriers we sometimes assume that customers are aware of standard accessorial charges for waiting time, tailgate, cube or any number of things that should affect a freight rate. Problem is that unless it is spelt out the customer will probably not agree to paying.
Always a good idea to have a standard one page list of your extra charges. Have the customer sign it when you first start doing business and stick it in thier file. It will come in handy some day.