California truck drivers at three major transportation companies went on strike Monday morning, demanding an end to purported labor law violations such as misclassification and intimidation. This is the fourth strike initiated by the drivers with the backing of the Teamsters union, but it’s the first without a definitive end date; whereas previous strikes have lasted between 24 and 48 hours, the drivers are now saying the won’t return to work until their demands are met.

“We were fed up. It just got to the point where the drivers are done,” said Alex Paz, a former driver with TTSI, one of the three firms affected by the strikes. Paz, who was fired in late May, alleges that the firm retaliated against him after he spoke out regarding purported labor law violations.

Over 120 drivers will be going on strike at the ports of Los Angeles and Long Beach, two of the main supply arteries on the West Coast. Roughly 40% of all imports to the United States go through one of those two ports. The firms affected by the strike are responsible for shipping goods to major retailers such as Walmart and Target.

The National Labor Relations Board filed a complaint against one of those firms, Green Fleet Systems, in late June over allegations of intimidation and wrongful termination. But even more so than those charges, the key issue at stake in this dispute is alleged misclassification. The three firms affected by the strike – Green Fleet, TTSI, and Pacific 9 Transportation – classify their drivers as independent contractors instead of employees, meaning they don’t have to pay various benefits.

“When the company misclassifies you, you’re denied Social Security, you’re denied medical, you’re denied workers comp,” said Paz. He and the other strikers argue that they should legally be classified as employees, which would entitle them to those benefits and allow them to unionize.

Misclassification is endemic to the port trucking industry, according to a joint report [PDF] from the National Employment Law Project (NELP), the Los Angeles Alliance for a New Economy (LAANE), and the labor union coalition Change to Win. They claim that about 65% of the nation’s port truck drivers are misclassified by their employers, costing those drivers a collective $1.4 billion annually.