I assigned a task via email, using the MT model -- asking, providing deadline, reasons etc. A couple of weeks later in an O3, my direct informed me that my email was unreasonable, in that he and his support staff don't have time to provide the data requested, they're too busy. He went on to say that I should KNOW that they're too busy, and instead of assigning the task via email I should come and discuss it with him in advance to verify that there's time to complete it, so he understands the reasons for the request, etc.
I responded by saying that when I assign work I always assume that if the assignee anticipates having difficulty meeting the deadline, doesn't understand the task, or doesn't agree that the task should be performed, that I expect them to come to discuss it.
He rejected this, saying that it puts him in an awkward position, and that instead I should know capacity for performing the task before assigning it, and if I don't know if there's capacity, then I should ask. This to me seems tantamount to requesting permission to assign work, which I naturally disagree with.
I would appreciate any suggestions folks here might have as to how I can persuade my direct to understand my point of view and accept responsibility for managing their workflow without having to resort to role power.