My job had a voluntary opt in to union membership so it's not new or hard to organise. Upside of not joining is you save money and don't support the Labour Party, downside is you get no say in votes and no protection from the union to sort out grievances.
I was a member of the Musicians Union for a few years (bit of an anomaly there, it's also a trade association for self-employed musicians including part timers), opted out of the political levy but still got sent a form to vote for deputy leader of the Labout Party.
