Recently in the UK, transport workers have gone on strike, causing severe disruption as only 1 in 5 rail services are now running. They can only do this as a result of unionisation and laws protecting unions (for example, unions are not liable for damages they cause).
As a student of economics, I am unsure as to whether unions are a net benefit to society. I understand that it may help combat employers who have monopoly power, which is usually the case in public sector industries such as transport in London. At the same time, the workers are being paid on average between £70k and £80k (more than twice the UK average salary) for a job which could essentially be automated (as it is on other metro services). To me, this feels inefficient, but what economic methods / concepts would we use to assess whether a union is a good thing or a bad thing? Are there any textbooks which cover this well? Thanks.