Public sector unions are not anti-vaccine—there is nothing about vaccines in conflict with Labor Movement values. When public sector unions oppose vaccine mandates, it is to protect their members in the post-COVID future.
The core union worker protection on the job is the collectively bargained agreement with the employer--the contract. This contract has a scope, what can be bargained and what is left to management. Unions cannot use bargaining to make an employer produce widgets or plumbuses, but the contracts do say when the employer decides, a contract outlines the wages, benefits, job classifications, working conditions, and disciplinary procedures for doing either.
There are many different laws governing public sector unions across state and local jurisdictions so specifics vary. But in general terms, posit a public sector union with a legislature that just passes a law to mandate vaccination. The public sees one thing, but unions know the legislature is changing a contract’s scope unilaterally.
The problem for any union is, what will stop the same legislature coming back and mandating other changes to working conditions or even wages, based on the precedent set with a COVID mandate? While such mandates appeal to a pro-vaccine public, it is ultimately an attack on collective bargaining and an exercise in union busting.
This is the core of why unions sue, to protect members after COVID. Contracts always have a process where the employer and union members can negotiate changes and institute policies to a current contract for COVID safety. This has been done across the United States. A legislative mandate is not a negotiation, but an erosion of a contract’s scope that will lead to more acts of political expedience that will trump workers rights to a contract over time.
Union members and leaders reflect the broader society, and every local union has its share of vaccine hesitators and outright opponents. This is the real world in the United States today. Labor union members have their own individual opinions on a mandate and that shapes how democratic unions respond. But it is the institutional imperative of a union to preserve collective bargaining for the future that leads them to court.