Lot's of misconceptions about the scale of unionization in the Pittsburgh labor force. With the decline of steel and heavy industry, the rate of unionization in the labor force has dropped as well. Most still don't believe this when I point it out, but unionization among local workers is under 14% which places it about average among large metro areas.
Union membership as a percentage of total employment for the top 25 metropolitan statistical areas in 2007
And that is unionization among all workers. Private sector unionization is even lower for the region, around 10%.