One of these candidates is not like the other. On the same day Democratic presidential candidates appeared at the AFL-CIO conference, GOP hopeful Mike Huckabee made his pitch to the union.

Huckabee was the only Republican presidential candidate to appear. The AFL-CIO is still mulling its White House options.

The labor group unanimously voted last Monday to delay endorsing Hillary Clinton for the 2016 nomination. In recent weeks, Clinton has caused many labor activists to second-guess her intentions as she delayed taking a firm stance on key issues such as the Trans-Pacific Partnership and a $15 minimum wage.

Huckabee is running as a conservative, but claims that he will "never be the Washington-Wall Street candidate" and that he is fighting for those who have been left behind. The former Arkansas governor also went on to blast Obama's trade deal, the tax code and the federal deficit.

Huckabee's opposition to entitlement reforms he says will hurt the social safety net and support for trade restrictions have irritated many fiscal conservatives, but endeared him to blue-collar GOP conservative voters.

For the past 40 years, wages have remained flat for 90 percent of Americans, and since 2000 the United States has lost 5 million manufacturing jobs, closing over 60,000 manufacturing plants along with it, Huckabee argued in an op-ed on Wednesday. He also claimed that if Republicans are to win the White House in 2016, they must do better amongst Hispanic, African-American and union voters.

"I've been fighting for the forgotten long before it was the cool thing to do — particularly in the GOP," Huckabee said in the op-ed. "I won't agree with the AFL-CIO on everything, but I do agree that American workers have been getting punched in the gut and kicked in the teeth."

During the meeting, Huckabee stressed the importance of collaboration between labor unions and the Republican Party, citing the Trans-Pacific Partnership as an example. He also said that labor unions are not "the enemy" of the Republican Party.