Your comment makes some significant factual mistakes. For one - there was no contract before the union. There were appointment letters, but there was nothing really governing what could or couldn't be in them. Minimum salaries are not really covered by any sort of federal/state law (unless you're thinking of the minimum wage, which I really don't think applies), and the gain in salaries was not that postdocs were going to be told what they made, its that there were rules set up to make sure that postdoc salaries lived up to a minimum standard. Minimum salaries, guaranteed pay raises, etc.
And while it's good that your PI was paying for your healthcare, that was not universal by any means. Now all PDs have access to healthcare coverage at reasonable and fixed costs. You're right that most (all?) visas require health insurance, but that doesn't automatically mean you can afford it. Many postdocs were forced to buy bad travel insurance that didn't really cover anything other than catastrophic injury because they couldn't afford to pay what UC told them they had to. That was fixed by the union.
I agree that the 1 year appointment minimum seems excessively reasonable, but the truth is that many PDs had to deal with the administrative headache and job insecurity of month-to-month or rolling 3 month appointments instead of longer appointments.
Most postdocs at UC join the union and all postdocs at UC have and do benefit from it. While it's true that many postdocs are treated perfectly well, that number is increased by the efforts of the union and its members. The average postdoc makes 12% more than 5 years ago. That's not true outside the UC. The difference? Our union.