Teamsters, the union that represents thousands of Amazon workers across the country, said that "momentum continues to mount" as workers seek "fair treatment" from the online retailer.
Outside of the City of Industry facility Thursday, workers were heard chanting "Amazon you can't hide, we can see your greedy side." They say, among other things, they're asking for job security and better pay.
"We get no vacation, sick days. We've had workload that has substantially increased over the last six years that I've been working," said Vanessa Valdez, a delivery driver. "I'm not a greedy person. We're not greedy. We want what's fair for a full day's hard work."
Teamsters workers walked off the job Thursday morning at delivery hubs in City of Industry, Palmdale and Victorville. The union also represents workers from the San Bernardino facility.
Teamsters President Sean O'Brien joined striking members at the City of Industry facility on Friday.
The union said it launched a strike after Amazon ignored the deadline for contract negotiations on Dec. 15. They said Amazon refuses to recognize their union, affecting nearly 10,000 warehouse workers and drivers across the country.
The strikes extended across the country at seven different locations, affecting facilities in Southern California, New York, Illinois and Georgia.
The union is calling it the largest strike against the online shopping giant less than a week before Christmas.
"If your package is delayed during the holidays, you can blame Amazon's insatiable greed. We gave Amazon a clear deadline to come to the table and do right by our members. They ignored it," O'Brien said. "These greedy executives had every chance to show decency and respect for the people who make their obscene profits possible. Instead, they've pushed workers to the limit and now they're paying the price. This strike is on them."
In a statement to ABC News, an Amazon spokesperson claimed that most of the strikers are not Amazon employees.
"What you see here are almost entirely outsiders-not Amazon employees or partners-and the suggestion otherwise is just another lie from the Teamsters," an Amazon spokesperson said in a emailed statement Thursday morning. "The truth is that they were unable to get enough support from our employees and partners and have brought in outsiders to come and harass and intimidate our team, which is inappropriate and dangerous. We appreciate all our team's great work to serve their customers and communities, and are continuing to focus on getting customers their holiday orders."
Workers told Eyewitness News on Thursday that Amazon's claims simply do not make sense.
"We represent Amazon, we have to follow their strict guidelines and when we don't follow those guidelines Amazon can actually terminate us," said Richard Smith, member of Teamsters Local 396. "So we have two people that can actually terminate us, Easy Logistics and Amazon. So why do they have authority to discipline us when they're not our employer? That doesn't make sense."
Delivery drivers like John Gutierrez are not technically Amazon employees because they work for third-party logistics companies. And even though they say they recently voted to unionize, Amazon doesn't recognize them as union employees.
"It just doesn't sit right with me. How are you going to tell us we're not Amazon employees when we wear your stuff, we support you, we make Amazon look good," Gutierrez said.
Gutierrez says their workload is overwhelming.
"I want to say we have a minute to deliver every package, and we're forced to take our 30, some of us don't even take our lunches and stuff like that because it's so time-consuming... If you have to use the bathroom, some of us have to go pee in a bottle. Just for us to use the bathroom, we can't go 10 minutes without getting into trouble," Gutierrez said.
The union says the National Labor Relations Board has ruled that Amazon is a joint employer.
"We're branded from head to toe with Amazon. Our vans are (too). When I go knock on the door, I don't say, hey, I'm a DSP with Amazon. I say I'm Amazon," said Alfredo Muñoz, a delivery driver.
The National Labor Relations Board certified the election to unionize at one of the facilities in New York, while the other facilities have unionized by majority support without government-administered elections.
"This is not intentional to the mess of Christmas, but it's our livelihood, like we're fighting for our livelihood here," Muñoz said.
CNN Wire contributed to this report.