Sen. Bernie Sanders (I-Vt.) (Photo by Kevin Lamarque/Reuters)

CEDAR RAPIDS, Iowa -- Sen. Bernie Sanders, who's been a fierce voice for the working class on the presidential campaign trail, put some action behind his words Friday, joining a picket line outside a factory here.

Sanders, the independent senator from Vermont, marched with workers at the Penford Products plant, which produces potato starches, and where the union that represents them is locked in a bitter contact dispute with a new out-of-state owner.

"We are sick and tired of the war against working families," Sanders told scores of workers who gathered in a park next to the plant following the informational picket.

Echoing his lines on the campaign trail, Sanders, a self-described democratic socialist, decried "corporate greed," adding: "That's what we're seeing here. ... We have got to stand together and tell this company that greed is not acceptable."

Workers at the plant, represented by the Bakery, Confectionery, Tobacco Workers and Grain Millers Union Local 100G, are on the job without a contract but are threatening to strike if a deal is not reached with the new owner, Ingredion Inc.

Sanders's involvement in the local dispute comes as he and Hillary Rodham Clinton, the Democratic front-runner, are fighting for support among labor unions in Iowa and nationally.

[In union-heavy Nevada, Clinton and Sanders court divided labor]

Several of the participants in the picketing late Friday afternoon said Sanders's presence was a reminder of his authenticity on labor issues. Sanders has marched in solidarity with aggrieved workers throughout his career in politics, which includes stints in the U.S. Senate and House of Representatives and as mayor of Burlington, Vt.

"Bernie has shown that it's not about talking the talk,"Chris Eby, Local 100G president, told the gathering Friday. "It's about walking the walk."

As they awaited Sanders's arrival, the picketers cycled through several chants, including, "Hey, hey, ho, ho, the war on workers has got to go." Sanders was handed a sign when his car drove up and took his place in the line.

The event, which came amid a three-day swing for Sanders in the first presidential nominating state, was still fresh on his mind when he appeared at a rally at nearby Coe College in Cedar Rapids on Friday evening.

"What is going on here is exactly what has been going on all over the country," Sanders said, suggesting the labor dispute was among the reasons the country needs "a political revolution."

[Sanders draws more than 2,500 to Iowa stop — tops for this presidential cycle so far]

The rally, which college officials estimated drew 2,000 people, was one of the largest this cycle in Iowa. The largest to date remains a Sanders rally in Council Bluffs in July that was said to have attracted 2,500 people, including many from just across the state line in Nebraska.

Sanders's current Iowa trip, which began Thursday, is his first since a new poll showed him drawing close to Clinton in the state.