Collection boxes also were moved or locked, suspending mail locations from certain areas in Washington.
But a spokesperson for the federal mail service told Fox News that the process was a part of its protocol.
"It’s part of our normal procedures to keep our employees and customers safe during times of protest or when large crowds are gathered near postal facilities, on postal routes, or by mailboxes," the USPS said in a statement Saturday.
More than 15 different USPS locations have been were disrupted in D.C., with varying days of reopening.
D.C. will see massive street closures on Jan. 20 -- a normal security procedure for the swearing in of a U.S. president -- but this year security has been heighted to an unprecedented level with the deployment of 21,000 National Guardsmen and 5,000 active duty troops.
The increased security was adopted following the breach at the U.S. Capitol last week by thousands of Trump supporters, resulting in the death of at least five individuals.
But while impacts on the mail service in Washington may be common during a presidential inauguration, at least another 17 states also will experience closures, first reported CNN.
The FBI has warned about protests in every state capital on and around Inauguration Day, advising state and security officials to be on the guard for an increase in explosive devices.
A spokesperson for the FBI told Fox News that they are "supporting our state, local, and federal law enforcement partners with maintaining public safety in the communities we serve."
"Our efforts are focused on identifying, investigating, and disrupting individuals that are inciting violence and engaging in criminal activity," the FBI added in their statement. "As we do in the normal course of business, we are gathering information to identify any potential threats and are sharing that information with our partners.
"The FBI respects the rights of individuals to peacefully exercise their First Amendment rights," the statement added.
Stephanie Pagones contributed to this report.