Tanker trash / Halcyon
I don't refer to removing the pilot from the flight as being a hard call. Merely the method used. Again, I would directly suggest the affected crew member calls in sick, even stating to them my concerns; and if this fails I'd explain what I was then going to do: call in sick myself and contact my chief/fleet captain. Perhaps in the modern world that could be construed as masking the issue. However I'd like to give the individual the benefit of the doubt that they'd made a terrible error of judgement and I was doing them a favour.
The hard situation I refer to would be having that conversation with a colleague or taking it to the authorities directly.