In Europe unions are likely to take progressive political positions outside their main area of concern, which is collective bargaining in their sector. In the US unions are purely out to defend the interests of their members, progressive politics be damned. One example that struck me was that some union or professional association of American prison guards was vocally in favour of tough-on-crime policies leading to more incarcerations and hence more jobs for them. This goes beyond collective bargaining into influencing social policy in decidedy non-progressive ways (especially given how the criminal justice system is stacked against minorities and the poor), and is something I could not imagine a European union doing.

guaranteed to evoke a violent reaction from police is to challenge their right to "define the situation." --- David Graeber citing Marc Cooper