I’m familiar with sectoral bargaining in the abstract but wasn’t aware European workers had the ability to choose which union represented them in negotiations. How does that work in practice?
It is rare, but a workforce can even choose to move to a different union.
In a lot of countries, it's not much different than choosing a pension fund option. You join a job, you choose which union best represents you based on your industry/title/etc (if you are not already a member). If you are not happy with your current agreement, you choose a different union that promises better outcomes.
It's so much less extreme than US unionization. There's not much reason for hostility between business and unions - unions don't get these all or nothing powers like they do in the US.
Once a workplace is unionized in the US, members have no real say or transparency to the union negotiation process. The union reps do not even have to work at the facility (in many larger unions, they are professionals paid for by the union).
Elections are only union wide, not specific to the company. And there is not really any day-to-day advisory capacity. Unions reps only exist to enforce the contract as signed.
This solves a lot of problems with us unions, where they have a state sanctioned Monopoly on the workers.
The classic example is unions are going for terms that screw over junior members but there are other perverse examples. At my friend's company the Union demanded that it be forced to return to office because the larger number of field technicians we're a voting majority of the union and angry they couldn't work from home.
My understanding is German and Scandinavian unions are much more collaborative and are unlikely to force demands that bankrupt companies.
This is why unions have such a negative connotation in the US. A lot of people see municipal governments being held hostage by unions over pensions and early retirement, and union employees being so hard to fire that you end up with "rubber rooms" and end up associating unions with expensive enshittification of services.
24 states allow Union shops (workers must join the union after hire).
In theory multiple unions could strike together. Alternatively, dissenting members of a single union can keep working.
In both systems striking is the union leverage.
But that alternative of dissenting unions not striking is exactly the loss of leverage that I was talking about.
The story I always think of is the Port of Portland shutting down was because the ILWU organized a $20 million dollar slowdown to punish the operator. The operator ended up pulling out of the city never to return, costing all the ILWU workers their jobs, as well as the city of Portland a few million a year in taxes.
The reason for the $20 million dollar slow down? The ILWU wanted to take two jobs away on the site from the IBEW!
Take the NHS; it will have to deal with ten plus separate unions - https://nhsunions.org/#about – of which the biggest powers are the British Medical Association and the Royal College of Nursing, but the cleaners are GMB or Unite and they're huge pan-working-class institutions.
Education has to deal with the NEU, the NASUWT, and the NAHT, each of which has a different political slant. Some unions in the UK have been historically rather centrist in their politics (a good example of that is Prospect, https://prospect.org.uk/about/, which is a roll-up of a number of scientific and finance unions), some are firebreathing communists, but all of them work across employers.
There's also no such thing as a closed shop in the UK – because there are much stronger worker protections, there's less of a need for one.
(I was, at one time, in a majority-UCU workplace; https://www.ucu.org.uk.)