It happened at Gallery Pizza on Erial Road in Gloucester Township, New Jersey in May.
Since that incident, other stores throughout the region have reported getting fake bills.
"We have had five or six other similar incidents with $20 bills, $100 bills. We're looking into the possibility of them being related," said Lt. Paul Fisher with Gloucester Township police.
The owner of Gallery Pizza said his employee realized the bills didn't feel right after a suspect in a black hoodie paid for a slice of pizza and left.
When a second suspect tried to do the same thing, the employee checked the bills.
"The store employee marked the bill and saw it was fake, so she refused service to the second gentleman," said Lt. Fisher.
Police said the two men left together in a gray minivan with New Jersey tags.
This incident comes after two other reports of counterfeit bills being found in Chester County.
Police in West Chester, Pennsylvania, say two men there passed fake bills at a CVS on July 1.
WATCH | Police across Chester County search for suspects in counterfeit bills investigation
Police across Chester County search for suspects in counterfeit bills investigation
Then, on May 30, two men passed a fake $100 at a Star Gas and Diesel in Kenneth Square.
Authorities do not believe the two incidents across the two states are connected.
They are urging store owners to keep an eye out for counterfeit money.
"I would absolutely check all bills. Especially $20 and up," said Lt. Fisher.