1) Wage floors (this
is a problem in some parts of our industry. Game development, for instance. Maybe in other tech related fields like sysadmins? I'm less familiar.)
2) Healthcare benefits
3) Negotiating better IP control. Side projects, open source, etc. are locked down at various companies. There was a front page story about this today.
4) Better treatment for oncall. I know folks who have had to work for 17 consecutive hours for an incident and got nothing.
5) Better treatment for crunch -- tech workers in games have this particularly bad, but it's not limited to just that industry.
6) More control over how the company outsources/contracts with workers
7) All sorts of other side benefits that could be collectively funded -- union libraries, training, networks, publications, resources for new professionals, discounts on union developed software, etc.
8) Parental leave, sick time, and other basic benefits
9) Ensure and oversee processes to protect people who end up on the public stage. If you believe cancel culture is a thing, maybe having a union rep on hand and an established process for managing firings would be in your best interest.
10) Forced arbitration is another thing I'd consider talking with a union about.
11) Having a union rep on hand for HR proceedings