[doesnt_know]

I personally don't think ultimatums are a tool that you should ever employ in an employment situation outside of collective action.

You can just leave off the ultimatum and attempt to improve your situation by communicating it in a way that is directly actionable (I'd like to work on X instead of Y, can you arrange that?). You'll have your own internal deadlines of course, but you shouldn't communicate them.

[bluGill]

Ever is too strong, but remember the less often you give an ultimatum the more powerful it is when you do. When you have a long standing reputation (must come first) as a 'team player' a sudden ultimatum will get a lot of attention, but it will be years before you can give another.

if like many you switch jobs every few years you can never develop that reputation needed for an ulimatum in the first place. (Staying for years is never 100% in your power but some jobs have better chances of it)

[Buttons840]

The ultimate exists whether or not you communicate it. I would hope that with enough tact that truth could be communicated.

[hobs]

The main thing is that if someone isn't going to do something in normal circumstances, an ultimatum is really for yourself to be done with waiting.

[Esophagus4]

Just be careful - some will see it as having their arm twisted. You may get what you want in the short run, but in the long run, when you negotiate with leverage, people dislike that.

It is the nuclear option, and you will lose the trust of your leadership chain.