[avar]

I don't know about unions in the UK, but in some other European countries your union won't have anything to do with your salary negotiation or setting industry-wide salary ranges.

They might if you're in a teacher's union, or working in some minimum-wage job with a mandatory union.

But for any high-paying position like software engineering your union is there to have your back if you're being screwed over on your employment contract, to bust the balls of employers who worked you for 41 hours, but only paid out 40 etc.

It's essentially a form of collective employment insurance for your industry, for which you'd pay a small monthly fee.