Unions are definitely the primary driver. Construction unions in New York are using current contracts to pay for their pension liabilities. In other words, taxpayers today are paying for work that was done 30 years ago. This guy is sort of irritating if you have to read him for more than a few hours, but his blog is full of evidence and analysis on this topic.
https://larrylittlefield.wordpress.com/2018/08/15/an-open-se...