This is an incredibly bold claim, can you cite this?
https://www.nytimes.com/2017/12/28/nyregion/new-york-subway-...
It's not just unions, but here is a taste:
There are “nippers” to watch material being moved around and “hog house tenders” to supervise the break room. Each crane must have an “oiler,” a relic of a time when they needed frequent lubrication. Standby electricians and plumbers are to be on hand at all times, as is at least one “master mechanic.” Generators and elevators must have their own operators, even though they are automatic. An extra person is required to be present for all concrete pumping, steam fitting, sheet metal work and other tasks.
In New York, “underground construction employs approximately four times the number of personnel as in similar jobs in Asia, Australia, or Europe,” according to an internal report by Arup, a consulting firm that worked on the Second Avenue subway and many similar projects around the world.
I don't know the answers. Some of them legitimately may be useless sinecures, but it's worth keeping in mind that what looks like redundant waste is sometimes an important guard against some kind of failure. Just because it isn't always used doesn't mean that it's not worthwhile.
Even more likely is that the redundancy exists because of something bad that happened in the past. That is how most regulation comes into existence.
Companies will want to save money and you don't need to force them to save money.
It's clearly a "job saving" argument and not a "money saving" one.
In the public sector, unions and engineering firms/management contractors are not at odds as they are in the private sector, they collaborate to rip off the public.