“What you see here are almost entirely outsiders — not Amazon employees or partners — and the suggestion otherwise is just another lie from the Teamsters,” Amazon said in a statement.
It was not clear how many people were participating in Thursday’s action.
The Teamsters union said thousands of Amazon workers were involved.
Overall, the group claims to represent “nearly 10,000” Amazon workers, after signing up thousands of people at about 10 locations across the country, many of them in the last few months.
The organisation has demanded recognition from Amazon, accusing the company of illegally ignoring its duty to negotiate collectively over pay and working conditions.
“They’ve pushed workers to the limit and now they’re paying the price. This strike is on them,” said the union’s general president, Sean O’Brien.
“If your package is delayed during the holidays, you can blame Amazon’s insatiable greed.”