Tens of thousands of trade unionists and their supporters are set to hold a demonstration in Philadelphia.
But many within the US labour movement admit that it is in trouble in some states.
The unions suffered a massive political blow last year when public sector workers were stripped of their collective bargaining rights in Wisconsin.
They have also been criticised for being slow to embrace the Occupy Wall Street movement.
Now, some say that to be successful, unions need to alter their relationship with power and big business.
Al Jazeera's Scott Heidler reports from Philadelphia.