Crediting unions solely for pursuing the creation of federal workplace safety regulations is a bit of a revision. It was a issue of significant public interest in the late 60s, and the specific reason that OSHA ended up being created was that Nixon had made a campaign promise to address workplace safety.
But regardless of the history, it’s not longer especially relevant to the roles of unions today, and certainly adds nothing to the value unions supposedly provide to their members.
I didn't credit them solely. Yes workers and workers right organizations supported it. Unions were the main ones lobbying it. We all know that without lobbying things don't get done in the US (unfortunately).
The question wasn't about what unions do today. The question specifically asked what unions were for. I stand by my statement that they were formed not only for pay increases, but also for working conditions improvements.
Who do you think lobbied to start OSHA? It was the unions.