The store on the corner of New Hampshire Avenue and Route 7 in Boston, Massachusetts, on Friday.
The store has been a source of concern for some drug policy experts and drug policy advocates since last week when a pharmacy worker tested positive for fentanyl.
The Massachusetts State Police have been investigating the Walmart drug testing lab.
The investigation was expanded to include a second worker.
The store is on a busy street, and most customers drive in, said store manager Jim DeSimone.
The pharmacy workers are also employees, so they’re not a target for any criminal activity, he said.
“They are not being targeted,” DeSimon said.
“They are just getting paid for their work.”
He said he believes the pharmacy worker was testing positive because they’re part of a family pharmacy and she was in a hurry, he added.
The company says its policy is to test all of its employees and employees of its drug testing service for drugs when they get on the job, and then notify the employee’s supervisor.
The pharmacy workers say they have received a letter from the company, but no one has reached out to them.
The investigation has also led to a new drug-testing policy at Walmart stores in Ohio and Texas.
The drug-sniffing dog, a 10-pound black Labrador, was on the front lawn of the store on Friday afternoon when a customer came by.
The customer said he was suspicious of the dog because he said he saw a dog around the store.
When a store employee arrived, the dog alerted him to the presence of drugs and the dog, which was trained to smell them, was sent off to the drug-detection dog, DeSimones said.
The dog is being tested for drugs in both locations.
The dog has not yet been released from the dog control facility.
The chain said it is working with state police and the Boston Police Department to find out who was responsible for the drug test.
“The investigation is still ongoing and we will continue to do everything we can to prevent a recurrence,” a Walmart spokesperson said in a statement.
“We have zero tolerance for drug use in any form, and our employees and our community are our priority.”
A Walmart spokesperson also confirmed that the dog was trained specifically for the purpose of detecting drugs.