Big Labor's AFL-CIO is a rock in changing times, Sen. Elizabeth Warren told the union federation during its 2013 convention.

“When political injustice threatened to break our democracy, members of the labor movement were there, working for jobs and freedom, marching right alongside Dr. Rev. Martin Luther King,” the Massachusetts Democratic freshman senator said.

That’s not quite true, though. While some unions, most notably the United Auto Workers, did back King, the AFL-CIO itself kept its distance and declined to support the historic 1963 March on Washington.

Only two years before, its executive council publicly censured A. Philip Randolph, president of the Brotherhood of Sleeping Car Porters and a key organizer of the 1963 march, for “unfair and untrue allegations” of racism within Big Labor.

That was when the AFL-CIO was a much more culturally conservative – some would even say reactionary – institution.

Warren’s airbrushing of history aside, it is impossible to imagine the labor federation doing such things today.

The AFL-CIO has changed a lot in the last half-century. One of the main ways it has changed it that it is no longer the predominantly white male organization that is fixed in popular imagination.

It changed even further Monday when convention delegates passed “resolution five” by a near-unanimous voice vote.

Resolution five called on the AFL-CIO leadership to make membership “available to any worker who wants to join the labor movement and who is not already covered by a collective bargaining agreement.”

In other words, they were formally inviting members of other liberal groups, most notably the NAACP, the Sierra Club and the National Council of La Raza, into the labor movement.

The details remain to be worked out with a constitutional amendment to be done. The nonunion members may only be invited to join a labor-backed activist group called Working America. They would nevertheless pay AFL-CIO dues.

Still, this represents a major shift: The leader of the U.S. labor movement is saying it will no longer solely be about labor. Not everyone is thrilled by this.

“We are supposed to be representing workers and workers' interests. We are not going to be the American Federation of Progressive and Liberal Organizations,” Harold Schaitberger, president of the International Association of Fire Fighters, told the Hill prior to the vote.

But even the IAFF did not actively oppose the resolution.

The days when the archetypal union member was a hardhat-wearing construction worker are fading fast.

In 1973, 40 percent of construction workers were unionized. Today, the number stands at just above 13 percent.

Public sector unions are filling in the gap. They represent 7.3 million government workers, edging out private sector unions, which now have just seven million members.

The AFL-CIO has embraced the change, touting that its delegates to this year's convention are 46 percent women or minorities. A movement that once viewed immigration with suspicion now backs the Senate’s reform bill.

A resolution adopted Sunday said: “A diverse and inclusive labor movement is essential to… representing the workforce of the future, where women workers, workers of color, LGBT (lesbian-gay-bisexual-transgender) workers and young workers are the clear majority.”

Despite such expressions of inclusiveness, one convention speaker, UCLA Labor Center Director Kent Wong, said Sunday, "the leadership bodies of the American labor movement are still too male, too pale, and too stale… It hurts us all."

Such attitudes help explain the labor movement’s shift to more actively engage with other liberal and progressive groups: Their memberships now increasingly overlap. So why not join together even more tightly?

Schaitberger’s remark about the AFL-CIO becoming the “American Federation of Progressive and Liberal Organizations” may yet prove to be prophetic.