Amazon employees are now barred from accessing buildings and working areas if they are not scheduled to work that day, the company announced.
The policy shift comes amid a feud with unions, who have criticized the policy as potentially hindering their ability to hold union drives and meetings.
Employees are also barred from accessing the buildings before or after their shift, under the new policy.
"There’s nothing more important than the safety of our employees and the physical security of our buildings," Amazon spokesperson Kelly Nantel said. "This policy regarding building access applies to building interiors and working areas."
The spokesperson said off-duty employees are not prohibited from meeting with co-workers in "non-working areas" away from the company’s facilities.
Amazon said the new off-duty policy "will not be enforced discriminatorily" to punish union efforts.
The move comes on the heels of a vote by Amazon workers at a warehouse on Staten Island, New York to unionize in April.
The new policy, enacted Thursday, could hinder union organizers’ efforts to meet with co-workers, they said.
Rev. Ryan Brown, an Amazon warehouse worker in Garner, North Carolina, who is trying to get his warehouse to follow Staten Island’s vote, called the new policy "a direct response" to unions.
"On our days off, we come to work and we engage our co-workers in the break rooms. This was a direct response to that, to try to stop organizing by any means necessary," Brown said.
Amazon explained the new policy as a safety concern.
"One part of this is knowing who is in our buildings at any given time, so we can quickly find and account for everyone in the event of an emergency," a notice to employees said.
The Associated Press contributed to this report.