The store manager asked a police officer to question Sherell Bates, who is 34 weeks pregnant.
In an e-mail, Staples told ABC affiliate WSOC that "As an organization, we would like to apologize to the customer."
Bates said she would rather have heard that apology in person rather than through the news, which is where she found out about the store's decision to terminate the manager.
"I actually saw it on social media," she said. "It wasn't directly to me - I didn't have any direct communication with Staples."
Bates was shopping for school supplies and about to check out when the officer asked her to step aside, where he then asked what was under her shirt and whether she was shoplifting.
"Initially, I thought he was joking, so my response was, 'Twins,'" Bates said. "I'm 34 weeks with twins. I'm having a boy and a girl."
Bates said the officer didn't believe her the first time, and he asked her again.
"At that point, to avoid him asking me again, I actually lifted my shirt just a little bit, just to expose my belly, so he could see that I'm just a regular pregnant person buying school supplies," Bates said.
"Staples has conducted a full investigation into the matter, and determined that the manager in question did not follow correct protocol and also failed to adhere to our existing policy on how to interact with our customers," the company said in a statement. "As a result of this finding, the manager has been terminated and Staples has apologized to the customer."
Bates said she's not inclined to continue shopping at the office supply chain.
"I think this was enough to deter me from spending my hard-earned money at that establishment," she said.