Oct. 5, 2011 -- The cavalry arrived in Lower Manhattan.

Representatives from at least 15 of the country's largest labor unions joined the Occupy Wall Street protesters for a mass rally and march yesterday in New York City. The "Union March" drew thousands and appears to be the movement's largest yet.

As of Thursday morning there had been reports of at least 30 arrests in various locations around Wall Street. Eight people were booked on Wednesday after protestors rushed the police line set up to keep them off the iconic street. They were met with pepper spray and rolling batons before being carted off.

"They tried to storm the barricades," a senior police official told ABC News New York affiliate WABC.

Earlier today, the AFL-CIO, United Auto Workers , and Transit Workers' Union were among the groups that stood in solidarity with the hundreds of mostly young men and women who have spent the better part of three weeks sleeping, eating, and organizing from Zuccotti Square.

Their arrival was touted as a watershed moment for the "Occupy" movement, which has now seen copycat protests spring up across the country. And while the specific demands of the "occupiers" remain wide-ranging, the presence of the unions – implicitly inclined to making more direct demands – may sharpen their focus.

Today's rally and march began at 3 p.m., when the protesters marched approximately one mile north to Foley Square, where they met community and labor leaders. Then, at 4:30 p.m., they walked together back down toward Wall Street.

Republican presidential candidate Mitt Romney, speaking at a retirement community in Florida on Tuesday, denounced the movement. "I think it's dangerous, this class warfare," he said.

While some on the ground welcome the concept of a showdown with the "1 percent," organizers (who claim to represent "the 99 percent" of Americans they say are being trampled on by the financial elite), say they remain committed to "non-violent" protest.

Labor Unions' Impact

The question for today, though, is what affect the presence of labor unions will have on the tenor of the movement. To date, Occupy Wall Street has set their agenda during twice-daily "general assemblies" with large-scale votes and directly elected "working groups."

The unions do not operate this way. They are top-down organizations. Their leaders, though elected, make most decisions autonomously. They are well-versed in fashioning specific appeals, the very concept of which runs counter to Occupy Wall Street's purposefully abstract message.

"Think Facebook or Twitter: These protesters have adopted that same decentralized structure, Columbia University political science Professor Dorian Warren told ABC News Tuesday. "There's no one leader. It's not top-down. It's much more democratic, much more 'open-source.'"

"One of the beautiful things about [Occupy Wall Street]," says Yochai Benkler, co-director of Harvard University's Berkman Center for Internet and Society, "is that it is a movement defining itself as it 'becomes.'"

While the concept of "becoming" or "creating space" for dissent, as organizers preach, might seem a bit far off to grizzled union vets, it's a bedrock of the "Occupy movement." But to the hundreds who've made their beds on Zuccotti Park's stone encampment the meta-narrative probably seems a little bit beside the point. Whatever the risks entailed in opening up their action to different groups, with different acting ethics, they're happy for the new support.

But as history reminds, there's no such thing as "free love."

ABC News' Richard Esposito contributed to this report.