Truck drivers who haul cargo at the ports of Los Angeles and Long Beach are on strike again this week - this time with some new comrades on their picket lines: warehouse workers.

Workers from California Cartage, a warehouse at the Port of L.A., have joined striking truckers who drive for Pacific 9 Transportation and XPO Logistics, creating the potential for disruption at two key links in the cargo supply chain.

The port truckers have gone on strike repeatedly in recent years, mainly protesting that the companies they drive for are misclassifying them as independent contractors, rather than designating them as permanent employees. The workers want to be paid an hourly salary and benefits. Their campaign is backed by the Teamsters Union, which is seeking to organize truck drivers in U.S. ports.

Adding warehouse workers to the port truckers' campaign represents a new step for the Teamsters. The union's International President James Hoffa was in Southern California Tuesday to join picketers and talk to reporters at the Port of Long Beach.

Hoffa said half of the Teamsters 1.4 million members are drivers, and he estimated that the union already represents about 200,000 warehouse workers.

"Warehouse is a tremendous area, more opportunity," he said. "We'll be doing Cal Cartage - that's a beginning. We'll find other targets."

Harley Shaiken, a professor at UC Berkeley who studies labor says the Teamsters strategy is “innovative” and could prove advantageous.

“What this does is it looks at all of the logistics chain, or at least a critical part of it as one entity, and that gives a union considerably more leverage,” Shaiken told KPCC. “I think we well could see the Teamsters organize more warehouse workers as well as the continuing focus on the port truckers. The issues are a bit different but they’re both clearly in the same industry.”

The warehouse workers at California Cartage walked off the job for a few days last month, demanding higher wages. They've also filed a lawsuit against the company, arguing it owes the workers millions of dollars in wages and overtime. The workers argue that because Cal Cartage leases property owned by the City of Los Angeles, they should be paid L.A.'s mandated "living wage" - a few dollars per hour above the state's minimum wage - and they haven't been.

"We came together about a year ago to improve our conditions at the warehouse," said Anthony Vallecillo, who loads and unloads cargo at Cal Cartage's Wilmington warehouse. He explained that he and most of his co-workers are hired through a staffing agency. After three years of regular work at the warehouse, he is still a temp. "I got involved because I was tired of struggling to provide for my son and wife."

Vallecillo joined Hoffa and other Teamsters officials at the picketing site in the Port of Long Beach. He announced that he and some co-workers at Cal Cartage would walk off the job again on Wednesday. Teamsters officials estimated about 500 people work in the Cal Cartage warehouse during busy times, but they didn't know yet how many of those workers have decided to join the walk-out.

California Cartage did not immediately return calls seeking comment.

"We want the warehouse workers to know that we have their back," said Barb Maynard, spokeswoman for the port truckers' campaign. "The supply chain is just that: each link is connected together, and the Teamsters have absolutely realized that."

Weston LaBar, executive director of the Harbor Trucking Association, which represents trucking companies at the Ports of L.A. and Long Beach says his group hasn't taken a position on the California Cartage matter. But he is not surprised the Teamsters are turning their sights to warehouse workers.

"[The Teamsters] have an unfunded pension liability that they have to deal with, and they are trying to get as much membership as possible in order to fund that pension," LaBar said. He added that the union would continue to struggle to organize the majority of port truck drivers because the "independent contractor" model remains popular with drivers at a time when the ports face a shortage of drivers.

"We’ve got opportunities for folks no matter if they want to be an independent contractor, an employee or an employee that’s part of a labor union," LaBar told KPCC. "Most of them continue to prefer to be independent contractors, or at least to be on a path to where they can become one eventually."

But Peter Dreier, a political science professor at Occidental College who tracks labor movements says the Teamsters have successfully organized a few trucking companies that operate at the port. He said the Cal Cartage warehouse workers have organized mainly on their own, but with the Teamsters and truckers behind them, the dynamic at the ports could change.

"They're not threatening to shut down the port. What it's going to do is to potentially shut down the abusive employer, particularly Cal Cartage," Dreier says. "The port does not want to have to deal with companies that are on strike."