To ask if its ever OK to pushback on a senior managers decision?

[TreatTreat]

One of the people I line manage has asked if it's ok if he does something which is very much out of his remit. Time is precious and services are pushed so I said no to this, however a senior manager who my colleague had also asked said yes. This will mean that this piece of work that doesn't sit with him, and will take up precious time, will then get passed to another colleague who's remit it does fit further up the line.

When I pushed back slightly on this, senior manager basically said colleague is doing it and that is final, but it's not colleagues job!!!

I wasn't given any rhyme or reason why this decision has been made and to be honest I am pissed off. I feel like I've been undermined as his line manager and that my thoughts on the matter haven't been taken into consideration at all. Wibu to tell senior manager this?

So your team member will be busy doing something else and won't be doing his usual work?

I think it's reasonable to ask senior manager if he can provide additional resources to support the fact that you now don't have capacity in your team.

Absolutely. But not in a push back ‘I feel undermined’ whingy way. More in a I was asked and I said no because <list concerns> can senior manager propose a way to mitigate these concerns or accept the risk / consequence etc

I think it would be reasonable to state your case, but don't expect the conversation to go well, given that he said colleague "is doing it and that is final". He doesn't sound like the kind of person who is mindful of the opinions/thoughts/input of others.