Can't tell them when they are not around conveniently.
True, but there is a chain of command. That chain goes up, above the Manager, or down to the Opps manager, supervisors, etc.
I'm not going to go on and on about it, but a couple points are worth mentioning.
1) NO one at FedEx Freight has the authority to tell the driver they must do anything which is unlawful, unsafe, or against actual Company Policy. Let that sink in just a bit...
2) Anyone who does pressure a driver into skirting the regulations, is putting that driver, the public, and the Company reputation, at risk. Such a person shows little respect for you, and deserve little in return. Education MIGHT change that.
3) If the driver fails to exercise their authority to say no, the situation will continue, uncorrected, with potential harm to others...
If ever in doubt, call The Main Office,
before you do it.
With so many variables, degrees of insanity, and motives, specific questions on how to proceed could be done though the
inbox, above, if confidentiality matters...