An AFL-CIO poll reveals union support for Donald Trump is waning. Pictured: Drivers for both Uber and Lyft call for union elections in New York City on Sep. 27, 2016. Getty Images

Donald Trump has positioned himself as the champion and voice of the middle class throughout his campaign, but his support among union members does not reflect that idea.

A poll of the American Federation of Labor and Congress of Industrial Organizations (AFL-CIO), the largest federation of unions in the United States, reveals union support for Trump is waning. The poll, which was released Friday, found that just 33 percent of union members nationally plan to vote for the GOP nominee. That number represents a sharp decline from the same poll in June, when Trump's share of union support was 41 percent.

In a press release accompanying the poll, AFL-CIO political director Michael Podhorzer wrote that the cause of Trump's bleeding of support from union members was Trump's track record of abusing labor.

"Union members now know that Trump outsources his products and uses low-quality Chinese steel in his buildings. Union members now know that Trump has routinely stiffed people working for him, and he won’t negotiate with newly unionized workers at his property in Las Vegas," Podhorzer wrote. "Union members will vote for Hillary Clinton, and a better future."

The AFL-CIO has made no secret of its opposition to Trump. The organization has joined the American Federation of Teachers, AFSCME, the National Education Association and various other labor unions to organize a large ground game effort in swing states to canvass in support of Democratic nominee Hillary Clinton. They are handing out a detailed script to their nearly 2,000 canvassers, instructing them to "make a personal connection" and highlight Trump's disparaging comments about minorities and immigrants.

The campaign seems to be working. The AFL-CIO poll found that, since June, Trump's support among union members has dropped 11 points in Ohio, nine points in Pennsylvania and seven points in Florida. He is now lagging behind 2012 GOP nominee Mitt Romney in union member support nationally.

One of the cornerstones of Trump's campaign has been his appeal to the working class and his promise to bring outsourced manufacturing jobs back to the U.S. He has vowed to impose heavy tariffs on companies that ship jobs overseas and renegotiate or back out of trade deals that do not benefit American workers.

"America has lost nearly one-third of its manufacturing jobs since 1997, even as the country has increased its population by 50 million people. At the center of this catastrophe are two trade deals pushed by Bill and Hillary Clinton," Trump said during a major economics speech in June. "Hillary Clinton unleashed a trade war against the American worker when she supported one terrible trade deal after another – from NAFTA to China to South Korea. A Trump Administration will end that war by getting a fair deal for the American people."