"The illegal sale or display of counterfeit goods or copyrighted materials costs the United States numerous jobs and billions of dollars a year," Edwin Hill, international president of the electrical workers group, wrote in a letter last week.
The AFL's Mark Ayers said copyright infringement hurts workers in industries such as book publishing, computer software, sports leagues, entertainment, clean energy, pharmaceuticals and electronics manufacturing.
But the bills have caused a massive backlash as Internet companies and consumer advocacy groups warn they could stifle innovation and lead to censorship of the Web.
"It is a shame the unions don't recognize the nature of the bills goes far beyond what is necessary to protect the jobs of their members," said Art Brodsky, a spokesman for consumer advocacy group Public Knowledge. "There are ways to combat what the industry sees as piracy without extending the reach of the U.S. to every website in the world nor giving companies the authority to shut down websites' financial support without any judicial rulings or even the hint of proof."