The city’s most experienced agitators—the labor and community groups that typically organize local marches, rallies and sit-ins—have been largely missing from the Occupy Wall Street protest that is in its 13th day at Zuccotti Park in lower Manhattan.

But that’s about to change.

A loose coalition of labor and community groups said Thursday that they would join the protest next week. They are organizing a solidarity march scheduled for Wednesday that is expected to start at City Hall and finish a few blocks south at Zuccotti Park.

“It’s a responsibility for the progressive organizations in town to show their support and connect Occupy Wall Street to some of the struggles that are real in the city today,” said Jon Kest, executive director of New York Communities for Change, which is helping to organize the march. “They’re speaking about issues we’re trying to speak about.”

Despite the common cause, the city’s established left did not initially embrace the protest, which began Sept. 17 and has been made up mostly of young people angry about the widening income chasm in the country, the growing influence of money on politics and police brutality, among other issues.

But as the action nears the start of its third week, unions and community groups are eager to jump on board. They are motivated perhaps by a sense of solidarity and a desire to tap into its growing success, but undoubtedly by something else too—embarrassment that a group of young people using Twitter and Facebook have been able to draw attention to progressive causes in a way they haven’t been able to in years.

The protestors have transformed the park into a village of sorts, complete with a community kitchen, a library, a concert stage, an arts and crafts center and a media hub. All of that has enabled them not just to sustain the action but to build momentum. And as celebrities like Michael Moore, Susan Sarandon, Russell Simmons and Cornel West have joined in, the city’s traditional activists have been forced to jump into the fray.

Daniel Massey [+] Enlarge

The protestors have transformed the park into a village of sorts, complete with a community kitchen, a library, a concert stage, an arts and crafts center and a media hub.

“It’s become too big to ignore,” said one political consultant.

Some of the biggest players in organized labor are actively involved in planning for Wednesday’s demonstration, either directly or through coalitions that they are a part of. The United Federation of Teachers, 32BJ SEIU, 1199 SEIU, Workers United and Transport Workers Union Local 100 are all expected to participate. The Working Families Party is helping to organize the protest and MoveOn.org is expected to mobilize its extensive online regional networks to drum up support for the effort.

“We’re getting involved because the crisis was caused by the excesses of Wall Street and the consequences have fallen hardest on workers,” a spokesman for TWU Local 100 said.

Community groups like Make the Road New York, the Coalition for the Homeless, the Alliance for Quality Education and Community Voices Heard are also organizing for Wednesday’s action, and the labor/community coalitions United New York and Strong Economy For All are pitching in as well.

Signs and chants will likely call for an extension of the so-called millionaires’ tax and a roll-back of state budget cuts. They will also likely show support for New York Attorney General Eric Schneiderman’s position that a proposed settlement between banks and attorneys general over troubled mortgage pools is too lenient.

Organizers of the march said they aren’t looking to take control of the Occupy Wall Street protest, which has captured headlines since it began nearly two weeks ago, but add to it.

“We’re not trying to grab the steering wheel or to control it,” said Michael Kink, executive director of the Strong Economy For All coalition. “We’re looking to find common cause and support the effort. It’s the right fight at the right time and we want to be part of it.”